Initiation of primary T cell--B cell interactions and extrafollicular antibody responses in an organized microphysiological model of the human lymph node

In vitro microphysiological systems (MPS) are needed to replicate events in the lymph node (LN) leading to humoral immunity against new immune threats, but current lymphoid MPS focus largely on recall responses from memory lymphocytes. Here, an LN MPS was developed from primary, naive human lymphocytes in microfluidic 3D culture to model interactions and antibody production at the LN T cell--B cell border. Naive CD4+ T cells exhibited CCL21-dependent chemotaxis, chemokinesis, and activation in the MPS, and were skewed to a T follicular helper (pre-Tfh) phenotype. IgM secretion was induced in co-culture with activated B cells in the presence of a superantigen, staphylococcal enterotoxin B (SEB); micropatterning confirmed that the interaction required physical proximity. SEB-dependence of IgM secretion was greatest at a 1:5 T:B ratio, while seeding more pre-Tfh cells accelerated plasmablast differentiation and clustering. On-chip co-cultures at a 1:5 T:B ratio developed large lymphoid clusters containing CD38+ plasmablasts and CD138+ plasma cells after 15 days, with response varying between donors. Significant plasmablast induction in T-B co-cultures did not require the pre-Tfh phenotype, but pre-Tfh cells were required for inducing IgM secretion. We envision that this LN MPS will enable predictions and mechanistic analyses of human humoral immunity in vitro.