Analysis of cells involved in germinal center reaction in Trypanosoma cruzi infection

GAZZONI, YAMILA; ALMADA, LAURA; MONTES, CAROLINA L.; ACOSTA RODRÍGUEZ, EVA V.; GRUPPI, ADRIANA

Banff

Congreso; B cell Renaissance: Epigenetics, Regulation and Immunotherapy; 2020

Germinal Centers (GCs) B cells can differentiate into antibody-secreting cells and memory B cells in response to T cell-dependent antigens. Within GCs, follicular helper T cells (Tfh) are crucial for affinity maturation. Other GCs-protagonists are follicular cytotoxic CD8+T cells (Tfc) whose function is not well established. However, it is known that Tfc share Tfh-related molecules.Our aim was to study the response of Tfh and Tfc, the GC reaction and the presence of plasmablast during T. cruzi infection. For this goal, C57BL/6 mice were intraperitoneally infected with 5.000 trypomastigotes (Tulahuén strain) and the frequency and number of the populations mentioned above were evaluated by flow cytometry at different days post infection (dpi) in the spleen and lymph nodes. Mice injected with PBS were used as control group.In the spleen, we observed that the peak of the Tfh (CD4+CXCR5+PD-1+ICOS+), Tfc (CD8+CXCR5+PD-1+ICOS+) and plasmablast (B220loCD138+) response was at 18dpi. In lymph node, the peak of Tfh and plasmablast response was at 23dpi while Tfc, at 18dpi. These responses preceded GC-B cells response (B220+FAS+GL-7+Bcl-6+) which peaked at 28 dpi. Tfc exhibited the higher frequency of cells specific for the immunodominant peptide TSKB20 and higher frequency of CD107a+ and IFN-gamma, TNF-alfa and Granzyme B producing cells than non-Tfc (CD8+CXCR5negPD-1neg) (p<0,05). Additionally, considering that IL-17A is a regulator of GC-B cell trafficking and of CD8+T cell survival, we also evaluated the expression of IL-17RA on GC-B cells, Tfh and Tfc. We observed that IL-17RA expression was higher in GC-B cells than other B cell subsets (p<0,05) and Tfc expressed higher levels of IL-17RA than Tfh (p<0,05), suggesting that IL-17 could influence cells involved in GC reaction in T. cruzi infection. To sum up, we observed an early plasmablast, Tfh and Tfc response and a delayed GC reaction in the infection with T. cruzi. Further studies are needed to understand the role of IL-17 in the GC reaction as well as whether Tfc are providing help to the GC-B cells or are controlling the infection in the follicle.