Molecular Immunology

Heat Shock Protein 70 (Hsp70) is a highly conserved and ubiquitous molecular chaperone that plays a central role in cellular protein machinery and stress response. Membrane-bound HSP70 has emerged as an important cancer biomarker and acts as a danger signal and elicits immune response. Hsp70 membrane expression is correlated to increased sensitivity to lysis carried out by NK cells. This study uses computational approaches to decode the interaction of Hsp70 with NK cells and determines the binding site for Hsp70 on the surface of NK cells. Our findings identified CD69 and NKP46 as the most probable binding sites for Hsp70. Additionally, we confirmed the strong binding affinity between Hsp70 and the CD94-NKG2A complex.

The formation of a stable peptide-MHC class II complex is a critical step in the adaptive immune response. In this work, we investigate the residue-residue contacts that anchor the peptide between the alpha and beta chains of MHC II and examine whether such anchoring residue-residue contacts are shared among different peptide-MHC II complexes. We hypothesize that there is a similarity between the map of contacts of antigenic peptides with the alpha and beta chains of MHC II and the map of contacts of the "natural" complex of MHC II with the CLIP - the fragment of the gamma chain. Thus, the CLIP-MHC II complex - specifically, PDB structure 3PDO - was taken as the prototype for peptide-MHC II interaction. To compare the contact maps between the prototype structure and antigenic peptides/MHC II in 14 crystal structures, we developed a unified numbering system for residues in peptide-MHC II complexes. Using this unified residue numbering system, we show that approximately half of the CLIP-MHC II residue-residue contacts have analogs in structures that involve different antigenic peptides and different MHC II (HLA-DR, HLA-DQ, and mouse A/B) alpha and beta chains. We present here this common network of contacts that underlies peptide/MHC class II interactions, as well as the structural and physicochemical characteristics of these contacts. Based on these shared characteristics, we propose criteria for the specificity of antigenic peptide loading into MHC II, whereby one can predict whether a particular peptide fragment will bind to MHC II as well as the likely localization of the fragment within the peptide binding groove of MHC II.

Despite the fact that the cell surface receptor HVEM (TNFRSF14) appears to be implicated in the development and progression of B-cell lymphomas, its specific role in these tumours is still unclear. On the one hand, HVEM over-expression is related to worse prognosis in some types of B-cell lymphoma and other solid tumours. On the other hand, most mutations of HVEM in B-cell lymphomas are thought to promote tumour growth through the loss of function. Here, we used a CRISPR-Cas9 system to study the effect of HVEM loss on gene expression in a murine model of A20 B-cell lymphoma (belonging to the diffuse large B-cell lymphoma group). We show that loss of HVEM does not affect the doubling rate of A20 tumour cells in culture, but leads to a decrease in BTLA expression. HVEM-deficient A20 cells do not present a different pattern of metastatic dissemination to lymphoid organs compared with unmodified A20 cells. However, we observed a significant expansion of endogenous B-cells as a result of A20 tumour implantation in the thymus. Although we found no differences in the dissemination or progression of HVEM-deficient A20 cells, our results reveal that loss of HVEM alters the leukocyte recruitment capacity of A20 cells in hepatic tumour nodules at the intermediate stage of tumour development, which may be of relevance as a mechanism of immune evasion.

The emergence of jaws in early vertebrates introduced a novel feeding apparatus and potent oral defenses but also increased the risk of physical injury and pathogen exposure. Innate immunity and inflammation constitute the bodys first line of defense against invading microbes and tissue damage, aiming to eliminate threats and restore internal homeostasis. Interferon regulatory factor 5 (IRF5) plays a critical role in orchestrating innate immunity and inflammation by regulating the transcription of genes that encode type I interferons (IFNs) and pro-inflammatory cytokines. Despite this, the evolution of IRF5 has remained poorly understood. We have identified the IRF5 and IRF6 genes in cartilaginous fish, including sharks. As cartilaginous fish represent one of the oldest surviving jawed vertebrate lineages, the presence of these genes suggests the genes have ancient origins potentially dating back hundreds of millions of years to early jawed vertebrates. Furthermore, our analysis shows that IRF5 has conserved nuclear export sequences and phosphorylation sites for activation throughout evolution from cartilaginous fish to humans, indicating these regulatory elements evolved early and have been maintained across jawed vertebrates. Additionally, the shift in subcellular localization of IRF5 from nucleus to cytosol, and of other interferon related IRFs, aligns with functional enhancements of IRFs in innate immunity and the emergence of IFNs across jawed vertebrates. This analysis implies that the evolution of jaws may have driven the emergence of new IRF members, the expansion of their functions, and the development of a unique inflammation and innate immune system.

Squamata exhibit a loss of genes for the gamma/delta T-lymphocyte receptor chains and a significant decrease in the number of V genes at the TRBV locus. Through genome analysis, I have discovered a new locus that contains V, J, C, and TM genes that have a similar structure to the classical TCR chains. This gene is viable, as demonstrated by the presence of messenger RNAs in the transcriptomes. Analyses using the AlphaFold2 program indicate that the deduced protein chain is associated with the alpha chain of the TCR. I have named this new chain "epsilon," and it forms a new TCR alpha/epsilon. Evolutionarily, the epsilon chain arose from a duplication of the beta chain gene at the time of the divergence of amphibians and reptiles and has since been specifically maintained in Squamata.

Cetaceans correspond to mammals that have returned to the marine environment. Adaptive changes are very significant with the conversion of the limbs into flippers. It is studied the changes that have occurred in immunoglobulins, MHC class I and II and T cell receptors genes. Constant regions of immunoglobulins are similar to those of the rest of mammals. An exception is the IgD gene, which is composed of three CH domains but CH1 similar to CH1 of immunoglobulin M. In the IGHV locus, it exist a decrease in the number of VH genes with the absence of genes within Clan I. The number of V{lambda} genes is greater than that of V{kappa}. In the genes for T lymphocyte receptors, it exists a decrease in the number of V genes with loss of significant clades and subclades. In V{beta} and V{gamma}, there is also the loss of clades. These declines of V, V{beta} and V{gamma} are not present Artiodactyla, and they are specific to Cetaceans. In MHC present tree evolutive lines of class I genes. These species have DQ, DR, DO and DM genes, but they are no present DP genes.

In teleost fishes there are three immunoglobulin isotypes named immunoglobulin M (IgM), D (IgD) and T (IgT). IgT has been the last to be described and is considered a teleosts-fish specific isotype. From the recent availability of genome sequences of fishes, an in-depth analysis of Actinopterygii immunoglobulin heavy chain genes was undertaken. With the aid of a bioinformatics pipeline, a machine learning software, CHfinder, was developed that identifies the coding exons of the CH domains of fish immunoglobulins. Using this pipeline, a high number of such sequences were obtained from teleosts and holostean fishes. IgT was found in teleost and holostean fishes that had not been previously described. A phylogenetic analysis reveals that IgT CH1 exons are similar to the IgM CH1. This analysis also demonstrates that the other three domains (CH2, CH3 and CH4) were not generated by recent duplication processes of IgM in Actinopterygii, indicating it is an immunoglobulin with an earlier origin.

Genes of the major class I and II histocompatibility complex have been extensively studied in mammals. Studies of these antigens in reptiles are very scarce. Here we describe the characteristics of these genes in the suborder Serpentes. We identified the presence of a much larger number of molecules of class I and beta chains of class II than found in mammals. Snakes only have one gene for the class II alpha chain. In these species, class I genes can be classified into two types. Approximately half of the genes lack 10 amino acids in the 1 domain, producing a structural alteration in the interaction region with the T lymphocyte receptor. In the genome of Thamnophis elegans, two haplotypes of an individual were studied revealing a different number and location of class I genes between these haplotypes. The results indicate that in these species, the diversity in the MHC is generated by the presence or absence of genes, independent of the presence of alleles.

Acinetobacter baumannii, Klebsiella pneumoniae and Pseudomonas aeruginosa are among the multidrug-resistant (MDR) Gram-negative pathogens that pose a growing threat, necessitating novel preventive measures in addition to traditional antibiotics. By using advanced immunoinformatics methods, highly conserved and immunogenic epitopes for B-cells and T-cells were selected from major virulence-associated proteins (LptE, YiaD, MrkD, PhoE, OprF, and Zot), which exhibited high antigenicity (VaxiJen scores 0.74-2.75) and 98.87% global population coverage. The construct vaccine comprises 50S ribosomal protein L7/L12 adjuvant and PADRE sequence for immunogenicity enhancement, with structural validation indicating stability (96.3% residues in the total allowed Ramachandran regions). High-affinity interactions with TLR2/TLR4 (binding energies: -1009.6 to -1079.6 kcal/mol) were found through molecular docking, and immune simulations suggested strong humoral (IgM/IgG) and cellular (IFN-{gamma}/IL-12) responses. Importantly, MEP vaccines can overcome major drawbacks of traditional vaccines by (1) offering cross-strain protection via conserved epitopes, (2) lowering the need for antibiotics through infection prevention, and (3) providing affordable options for healthcare systems affected by MDR infections. These findings demonstrate the MEP constructs potential as a preventative measure against nosocomial infections, which may have implications for combating the global AMR epidemic. Further experimental validation is needed to verify its efficacy.

Immunoglobulin Y (IgY) represents the major serum antibody in reptiles and birds, serving as the evolutionary precursor to mammalian IgG and IgE. While IgY diversification has been documented in several reptilian lineages, the structural basis underlying subclass divergence remains poorly understood. Here, we present a comprehensive phylogenetic and structural analysis of IgY sequences from 20 snake species, revealing two distinct evolutionary lineages (A and B) that arose through gene duplication. Structural modeling of the constant regions from Arizona elegans identified a fundamental difference in the light chain-heavy chain (CL-CH1) disulfide bond architecture between lineages. Lineage B utilizes CYS16 in the CH1 domain (alignment position 13) for the inter-chain disulfide bond with the light chain CYS98, whereas Lineage A employs CYS136 (alignment position 99), representing N-terminal versus C-terminal positioning within the CH1 domain. Analysis of 50 diagnostic amino acid positions between lineages revealed that changes are distributed across all constant domains (CH1-CH4), with 13 positions showing radical substitutions affecting charge or polarity. Sliding window dN/dS analysis demonstrated purifying selection ({omega} < 1) across both lineages, consistent with functional constraint following duplication. These findings provide structural evidence for subfunctionalization of snake IgY genes and suggest that alternative disulfide bond configurations may confer distinct biophysical or functional properties to each antibody subclass. This work advances our understanding of immunoglobulin evolution in reptiles and highlights the structural plasticity of antibody architecture.

Immunoglobulin M (IgM) is the most ancient and conserved antibody class in jawed vertebrates and is typically encoded by a single gene. In contrast, geckos and related lizards (infraorder Gekkota) possess multiple IgM genes within the immunoglobulin heavy chain locus. Here, we analyze 52 IgM constant-region sequences from 13 Gekkota species to clarify the evolutionary origin and functional consequences of this expansion. Phylogenetic reconstruction showed that IgM1 (the canonical form) is nearly monophyletic (86.7% clade purity), whereas internal-locus IgM2-6 variants display complex, lineage-specific duplication patterns. We identified 53 diagnostic amino acid positions distinguishing IgM1 from other variants, concentrated in CH1 (19 positions) and CH2 (25 positions). These differences are accompanied by a pronounced physicochemical shift in CH2: IgM1 carries a net positive charge (+2.01) while other IgMs are negatively charged (-2.13), a {Delta} of +4.14 charge units. Conservation analyses indicate stronger constraint on IgM1 in CH1/CH2, while internal-locus IgMs are more conserved in CH4, consistent with maintained polymerization function. Three-dimensional structural comparison of IgM1 and IgM4 supports functional divergence in assembly: IgM4 adopts an "open mouth" CH1-CH2 conformation with increased heavy-light chain contacts and a more electrostatically enriched interface, suggesting compensatory stabilization mechanisms. Together, these results support specialization of internal-locus IgMs through combined sequence and structural divergence.

Tetanus disease is caused by the spore-forming bacteria Clostridium tetani. Its development starts with wounds or mucous layers of spore contact in water, soil, human, and animal feces. It is prevented by vaccination, but the lack of booster shots throughout life and age-decreased immune surveillance by immunosenescence enforces prophylactic treatment in case of accidents. The disease incident and lethality present a high index in underdeveloped countries. In cases of infection, administering antitetanus antibodies is preconized, usually derived from immunized horses or humans. Heterologous sera origin and the total protein content represent risks such as serum sickness and serum sickness-like reactions. Human sera can carry unknown viruses. The search for human monoclonal antibodies (mAbs) against TeNT (tetanus toxin) has increased in the last few years, although none has been approved. From a panel of previously identified human mAbs derived from B-cell sorting, we selected two nonrelated mAbs that bind to HCR/T (fragment C) of TeNT, showing disruption of its interaction with the cellular receptor ganglioside GT1b. To gain more insight into the TeNT inhibition effectiveness, we present results based on cellular assays and molecular docking tools. We describe TeNT internalization in neurons derived from the neonatal rat spinal cord. Adding the single mAbs prevented TeNT internalization higher than 50% under a specific experimental condition. The data validation was performed by quantitative analysis of immunofluorescence punctate staining of Alexa Fluor 647 conjugated to TeNT. We also confirmed the Synaptic Vesicle Glycoprotein (SV2) mediator role in TeNT endocytosis. The molecular docking assays to predict potential TeNT epitopes of the mAbs showed the binding of both antibodies to the heavy chain of TeNT, specifically to the HCR/T domain. A higher incidence was found between N1153 and W1289 when evaluating candidate residues for conformational epitope. AUTHOR SUMMARYTetanus neurotoxin, produced by the bacteria C. tetani, is one of the most potent toxins. The ubiquitous presence of bacteria and spores in soil, water, and human and animal feces makes their elimination impossible, and accidents occur in contact with wounds. People who work in agricultural or animal production are more susceptible to infection. In recent years, there has been an increase in groups developing human monoclonal antibodies for specific immunotherapy. Our group screened a panel of monoclonal antibodies in search of the best neutralizing compositions. This work reports convergent in vitro and in silico results on two antibodies that bind to the toxin domain, which interacts with neuronal cells and initiates the disease pathway. We show the hydrophobic interactions and hydrogen bonds that make contact between each antibody and the toxin, the entry of the toxin into the rat primary spinal cord cells, its interaction with synaptic vesicle II, and how the antibodies reduce the entry of the toxin into the cells, pointing to their neutralizing potential.

MHC-I and MHC-II molecules are critical components of antigen presentation and T cell immunity to pathogens and cancer. The two monoclonal transmissible devil facial tumours (DFT1, DFT2) exploit MHC-I pathways to overcome immunological anti-tumour and allogeneic barriers. This exploitation underpins the ongoing transmission of DFT cells across the wild Tasmanian devil population. We have previously shown that constitutive expression of NLRC5 can induce stable upregulation of MHC-I on DFT1 and DFT2 cells, but unlike IFNG-treated cells, NLRC5 does not upregulate PDL1. MHC-II expression is crucial for CD4+ T cell activation and is primarily confined to haematopoietic antigen presenting cells. Transcriptomic analysis of DFT1 and DFT2 cell lines showed that several genes of the MHC-I and MHC-II pathways were upregulated in response to constitutive overexpression of the class II transactivator (CIITA) gene. This was further supported by upregulation of MHC-I protein on DFT1 and DFT2 cells, but interestingly MHC-II protein was upregulated only on DFT1 cells. The functional significance of the MHC upregulation on DFT cells was shown using serum from devils with natural or immunotherapy-induced DFT1 regressions; binding of serum IgG was stronger in CIITA-transfected cells than wild type cells, but was less than binding to NLRC5 transfected cells. This new insight into regulation of MHC-I and MHC-II in cells that naturally overcome allogeneic barriers can inform vaccine, immunotherapy, and tissue transplant strategies for human and veterinary medicine.

Spike (S) proteins are an attractive target as it mediates the binding of the SARS-CoV-2 to the host through ACE-2 receptors. We hypothesize that the screening of S protein sequences of all the HCoVs would result in the identification of potential multi-epitope vaccine candidates capable of conferring immunity against various HCoVs. In the present study, several machine learning-based in-silico tools were employed to design a broad-spectrum multi-epitope vaccine candidate against S protein of human coronaviruses. To the best of our knowledge, it is one of the first study, where multiple B-cell epitopes and T-cell epitopes (CTL and HTL) were predicted from the S protein sequences of all seven known HCoVs and linked together with an adjuvant to construct a potential broad-spectrum vaccine candidate. Secondary and tertiary structures were predicted, validated and the refined 3D-model was docked with an immune receptor. The vaccine candidate was evaluated for antigenicity, allergenicity, solubility, and its ability to achieve high-level expression in bacterial hosts. Finally, the immune simulation was carried out to evaluate the immune response after three vaccine doses. The designed vaccine is antigenic (with or without the adjuvant), non-allergenic, binds well with TLR-3 receptor and might elicit a diverse and strong immune response.

Oncorhynchus masou formosanus (Formosa land-locked salmon) is a critically endangered salmonid fish endemic to Taiwan. To begin to understand how its drastic change in lifestyle from anadromous to exclusively river-dwelling is reflected in its immune genes, we characterized the genes encoding six cytokines (IL-2A, IL-2B, IL-4A, IL-4B1, IL-4B2, and IL-17A/F2a) important for T cell responses as no genomic data is available for this fish. Interestingly, all genes appeared homozygous indicative of a genetic bottleneck. The IL2 and IL17A/F2a genes and their products are highly similar to their characterized homologs in Oncorhynchus mykiss (rainbow trout) and other salmonid fish. Two notable differences were observed in IL4 family important for type 2 immune responses. First, O. m. formosanus carries not only one but two genes encoding IL-4B1 proteins and expansions of these genes are present in other salmonid fish. Second, the OmfoIL4A gene carries a 228 bp deletion that results in a premature stop codon and hence a non-functional IL-4A cytokine. This suggests a reduced ability for T cell responses against parasitic infections in this species.

Understanding how the evolutionary relationship between immune cells and the blood-brain is important to devise therapeutic strategies that can regulate their critical function. In vertebrates, immune cells follow either a paracellular or transcellular pathway to infiltrate the BBB. In drosophila glial cells form the BBB that regulates the access of immune-like cells to the drosophila brain. However, it is still not known which route immune-like cells follow to infiltrate the drosophila brain. In vertebrates, paracellular migration is dependent on PECAM1, while transcellular migration is dependent on the expression of CAV1. Interestingly drosophila genome lacks both genes. Tre1 superfamily (Tre1, Moody, and Dmel_CG4313) play a diverse role in regulating transepithelial migration in drosophila. However, its evolutionary history and origin are not yet known. We performed phylogenetic analysis, together with HH search, positive selection, and ancestral reconstruction to investigate the Tre1 family Interestingly we found that Tre1 exists in mollusks, insects, ambulacria, and sclaidphora. Moody is shown to be a more ancient protein and it existed since cnidaria emergence and has a homolog (GPCR84) in mammals. The third family member (Dmel_CG4313) only exists in insects. The origin of the family seems to be related to the rhodopsin-like family and in particular family . We found that opsin is the nearest receptor to have a common ancestor with the Tre1 superfamily that seems to have diverged in sponges. We investigated the positive selection of the Tre1 family using PAML. Tre1 seems to have evolved under negative selection, whereas Moody has evolved during positive selection. The sites that we found under positive selection are Likely to play a role in the speciation of function in the case of Moody. We have identified an SH3, in Tre1 and, moody and Dmel_CG4313. Sh3 is known to play a fundamental role in regulating actin movement in a Rho-dependent manner. We suggest that Tre1 could be playing an important role in paracellular diapedesis in drosophila.

Dengue virus infection represents a major global health issue, with four distinct serotypes complicating the challenge of developing a vaccine due to the need for balanced, long-lasting immunity against all serotypes. Current vaccines have limitations, including an increased risk of severe dengue in seronegative individuals and moderate efficacy, highlighting the need for more effective solutions. Our study aimed to design a multi-serotype Dengue virus vaccine using a computational approach to achieve broad-spectrum immunity. We employed advanced computational tools and algorithms to predict B-cell and T-cell epitopes, ensuring the selection of antigenic targets that provide comprehensive protection against all four serotypes. The methodology included tools for B-cell epitope prediction, tools for MHC class II and I peptide predictions, and tools for toxicity and allergenicity screening to ensure the safety of the vaccine candidates. Our results identified 21 B-cell epitopes, 15 CTL peptides, and 12 HTL peptides, validated for safety regarding toxicity and allergenic potential. The vaccine construct incorporated the adjuvant {beta}-defensin-3 and specific linkers to enhance immunogenicity and stability. Tertiary structure prediction, Ramachandran plot analysis, and stereochemical examination confirmed the stability and quality of the vaccine model. These findings demonstrate the potential of computational methods in addressing the complex challenges of Dengue virus vaccine development. Our computational approach offers a novel pathway for vaccine design, potentially accelerating the development of effective multi-serotype vaccines. This study provides a promising foundation for future research and clinical validation, marking a significant step forward in dengue vaccine development.

In human tumor models we tried to identify and clone the TCR of tumor-reactive T cells enriched in mixed lymphocyte tumor-cell cultures (MLTC). In a particular MLTC, we identified a predominant TCR beta chain using the Beta Mark Vbeta Kit, but a corresponding alpha chain could not be amplified via RT-PCR using TRAV-specific forward primers. Therefore, we applied 5RACE to obtain the TCR alpha chain sequences. The 5RACE product revealed an alpha chain that encompassed 89bp of the TRDV1 5UTR, followed by the TRDV1 coding sequence joined in frame to TRAJ24. The ORF reaching from the TRDV1 start codon to the TRAC segment was intact, suggesting a functional TCR. To analyze this MLTC population in greater depth we conducted 10X VDJ sequencing. CellRanger identified the beta chain known from the Beta Mark analysis, but no corresponding alpha chain in the filtered results. The corresponding TRDV-containing TCR alpha chain could, however, be detected in the "all_contig_annotations" files. In a separate project, we performed TCR sequencing of tumor-infiltrating lymphocytes (TILs) in a murine tumor model. Also here, a predominant clonotype contained a TCR alpha chain joining Trdv2-2 in frame to Traj49. Transfection of both TCR cDNAs resulted in cell surface localization of TCR and CD3 as validated by FACS. Tumor recognition of the human, TRDV1-containing TCR could be demonstrated by IFNgamma ELISpot whereas the murine TCR did not recognize a tumor-derived cell line. TRDV-containing alpha chains have been reported in the literature for two HLA I-restricted TCRs against HIV peptides (Ueno et al, Eur J Immunol, 2003). To determine whether such TDRV-containing TCRs are unique events or whether Vdelta segments are commonly incorporated into TCR alpha chains, we queried the NCBI Sequence Read Archive (SRA) for 10X VDJ data and analyzed 21 human and 23 murine datasets. We found that especially TRDV1, Trdv1 and to some extent Trdv2-2 are more commonly incorporated into TCR alpha chains than some TRAV genes, making the TRDV segments a relevant contribution to TCR alpha diversity. For apparently solitary beta chains in 10X VDJ datasets, we suggest to scrutinize the "all_contig_annotations" files as these may contain an accompanying, TRDV-containing alpha chain.

Precursor B cell acute lymphoblastic leukemia (pre-B-ALL) arises as a result of precursor B cells acquiring driver mutations that lead to arrested differentiation and increased proliferation. Identification of driver mutations and understanding their biological function is critical to understanding pre-B-ALL development and advancing disease treatment. Using a mouse model of pre-B-ALL driven by deletion of genes encoding the related E26-transformation-specific (ETS) transcription factors PU.1 and Spi-B, we performed whole exome sequencing to identify secondary driver mutations. We identified recurrent variants in E26 transformation-specific transcription variant 5 (ETV5) resulting in R392P, V444I, and T505A amino acid changes. We found that the R392P and V444I variants altered the ability of ETV5 to bind to DNA using electrophoretic mobility shift assay. R392P and V444I variants did not activate a Dual-Specificity-Phosphatase 6 (DUSP6) reporter. In contrast, T505A ETV5 could interact with DNA and activate the DUSP6 promoter. To determine biological function, we forced expression of wild type, R392P, V444I, or T505A ETV5 in an interleukin-7-dependent pre-B cell line. Proliferation and apoptosis assays showed that T505A ETV5 conferred a proliferative advantage to pre-B cells. RNA sequencing showed that expression of ETV5 variants significantly altered gene expression in cultured cells. Through gene set enrichment analysis, T505A was suggested to downregulate the p53 pathway and the anti-proliferative protein, B cell translocation gene 2 (encoded by Btg2). In summary, these data suggest that ETV5 mutations play a role in pre-B-ALL by affecting proliferation and cell survival.

The protein heterodimer calprotectin and its component proteins, S100A8 and S100A9, play important antibacterial and proinflammatory roles in the mammalian innate immune response. Gaining mechanistic insights into the regulation and biological function of calprotectin will help facilitate patient diagnostics and therapy and further our understanding of the host-microbe interface. Recent literature has identified zebrafish s100a10b as zebrafish calprotectin based on sequence similarity, genomic context, and transcriptional upregulation during the immune response to bacterial infections. The field would benefit from expanding the breadth of calprotectin studies into a zebrafish innate immunity model. Here, we carefully evaluated the possibility that zebrafish possess a calprotectin. We found that zebrafish do not possess an ortholog of mammalian S100A8 or S100A9. We then identified four zebrafish s100 proteins-- including s100a10b--that are expressed in immune cells and upregulated during the immune response. We recombinantly expressed and purified these proteins and measured the antimicrobial and proinflammatory characteristics. We found that none of the zebrafish proteins exhibited activity comparable to mammalian calprotectin. Our work demonstrates conclusively that zebrafish have no ortholog of calprotectin, and the most plausible candidate proteins have not convergently evolved similar functions.