Authors
A Khan1; AF Francisco1; H Langston1; S Dey2; N Dey2; N Brown2; H Ashwin2; K Van Bocxlaer2; A Lima3; J Mottram2; JM Kelly1; PM Kaye2; MD Lewis1; D Perez Mazliah2; 1 London School of Hygiene and Tropical Medicine, UK; 2 University of York, UK; 3 Instituto de Biofisica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Brazil Discussion
Chagas disease, caused by infection with Trypanosoma cruzi parasites, is the most frequent cause of infectious cardiomyopathy in the world. Chagas heart disease (CHD), an inflammatory cardiomyopathy, develops in approximately one-third of chronically-infected people. Why some infected individuals develop cardiomyopathy while others remain asymptomatic for life remain poorly understood.
Here, we used experimental mouse T. cruzi infections with differing degrees of cardiac pathology to model different pathological outcomes observed in the clinic. We then used single-cell RNA sequencing (scRNA-seq), spatial transcriptomics and flow cytometry to identify immune signatures associated with differing degrees of CHD. scRNA-seq showed that TcVI-CLBR-infected-BALB/c (mild CHD) and TcI-JR-infected C3H/HeN (severe CHD) mice develop strikingly different immune responses to the parasite in the spleen, with B cells dominating these differences. Severe CHD lead to accumulation of an unswitched, recently-activated B-cell subset with very high expression of Nr4a1 (Nur77), previously identified as a marker of autoreactive B cells. To specifically track B cells reacting to the parasite vs those reacting to host cardiac tissues, we developed B-cell tetramers to detect, by flow cytometry and side-by-side, T. cruzi-specific and cardiac-specific B cells. Both parasite-specific and cardiac-specific B cell responses were robustly activated in the spleen of TcI-JR-infected C3H/HeN (severe CHD) mice. However, showing important differences in their functional profile, spleen-resident cardiac-specific B cells failed to develop germinal centre, class-switching and memory responses to the infection. Further, spatial transcriptomics of heart tissue sections showed a striking accumulation of plasma (B) cells dominating the immune infiltrate in the heart of TcI-JR-infected C3H/HeN (severe CHD) mice.
Thus, our data shows a dominant B-cell immune signature associated with severe CHD, characterised by accumulation of short-lived autoreactive cardiac-specific B cells in the spleen and striking accumulation of plasma (B) cells in the heart of infected mice. 
