B cell-stromal cell cross talk drives mesenteric lymph node eosinophilia during intestinal helminth infection

Eosinophils are involved in host protection against multicellular organisms including helminths and often participate in regulating long-lasting humoral responses. However, their recruitment to the gut-draining mesenteric lymph node (mLN), where they support the development of the adaptive immune response is still elusive. Here, we demonstrate the mechanism underlying the recruitment of eosinophils to the murine mLN post gastrointestinal helminth infection. We found that mLN eosinophils accumulated at immune interactive sites such as the interfollicular and paracortical regions in an IL-4R-dependent manner and was directly associated with the reduced availability of stromal derived eosinophil chemoattractants. Using multiplex imaging we confirmed that eosinophils associate within a stromal niche containing Lyve1+ lymphatic vessels, ER-TR7+Pdpn+ FRCs, and extrafollicular CD138+ plasma cells. Experiments utilising complete and mixed bone marrow chimeras demonstrated that mice lacking IL-4R expression or LT{beta} expression selectively on B cells had diminished eosinophilia and reduced extrafollicular plasma cell numbers within the mLN. When co-cultured with LT{beta}R activated FRCs, eosinophils gained an active phenotype with enhanced Il1rl1 (ST2) receptor expression. LT{beta}R ligation on FRCs resulted in enhanced IL-33 expression along with enrichment of distinct reactomes. Additionally, deletion of LT{beta}R in FRCs reduced the homing capability of eosinophils to the mLN, confirming the significance of lymphotoxin signalling in granulocyte recruitment. Overall, these results highlight the previously unknown role of B cell-stromal cell crosstalk in driving mLN eosinophilia and their potential role in regulating the quality and magnitude of the humoral immune response generated within the mLN.