CXCL13 expression in the gut promotes accumulation of IL-22-producing lymphoid tissue-inducer cells, and formation of isolated lymphoid follicles

The chemokine CXCL13 is overexpressed in the intestine during inflammation. To mimic this condition, we created transgenic mice-expressing CXCL13 in intestinal epithelial cells. CXCL13 expression promoted a marked increase in the number of B cells in the lamina propria and an increase in the size and number of lymphoid follicles in the small intestine. Surprisingly, these changes were associated with a marked increase in the numbers of RORgammat(+)NKp46(-)CD3(-)CD4(+) and RORgammat(+)NKp46(+) cells. The RORgammat(+)NKp46(-)CD3(-)CD4(+) cells expressed CXCR5, the receptor for CXCL13, and other markers of lymphoid tissue-inducer cells, such as LTalpha, LTbeta, and TNF-related activation-induced cytokine (TRANCE). RORgammat(+)NKp46(-)CD3(-)CD4(+) gut LTi cells produced IL-22, a cytokine implicated in epithelial repair; and expressed the IL-23 receptor, a key regulator of IL-22 production. These results suggest that overexpression of CXCL13 in the intestine during inflammatory conditions favors mobilization of B cells and of LTi and NK cells with immunomodulatory and reparative functions.

Most parasite-specific CD8+ cells in Trypanosoma cruzi-infected chronic mice are down-regulated for T-cell receptor-alphabeta and CD8 molecules

The present study shows that CD8+ T lymphocytes expressing low levels of T-cell receptor (TCR)alphabeta, CD8 and CD3 accumulate in the spleen, blood, peritoneum and liver, but not in the lymph nodes of mice chronically infected with Trypanosoma cruzi. Analysis of spleen lymphocytes reveals that most CD8LOW TCRLOW T cells have an experienced phenotype (CD44HIGH CD62LLOW and CD45RA,B,CLOW). These cells have small size, lack activation markers such as CD69, CD25 and CD11b (Mac-1), and do not spontaneously secrete cytokines, suggesting they are at the resting state. When stimulated in vitro with T. cruzi-infected macrophages, TCRLOW CD8LOW T cells behave as parasite-specific memory cells, readily responding with interferon-gamma (IFN-gamma) production. Indeed, among parasite-activated CD8+ lymphocytes, IFN-gamma production was mostly due to TCRLOW CD8LOW cells. Upon in vitro stimulation with anti-CD3/CD28 monoclonal antibodies, down-regulated cells produce IFN-gamma and tumour necrosis factor-alpha, but not interleukin IL-10 or IL-4. Our results indicate that despite parasite persistence, most T. cruzi-specific experienced CD8+ cells are resting. Nevertheless, when encountering infected macrophages these cells differentiate to Tc1 effectors.

Influence of acute-phase parasite load on pathology, parasitism, and activation of the immune system at the late chronic phase of Chagas' disease

To obtain low and high parasite loads in the acute phase of Chagas' disease, A/J mice were infected with 10(3) or 10(5) Trypanosoma cruzi trypomastigotes of the Y strain and treated on day 6 with benznidazol. One year later, chronically infected mice were screened for subpatent parasitemias, tissue pathology, and immune response. Mice infected with the high parasite inoculum showed higher levels of chronic parasitemias, heart and striated muscle inflammation, and activation of the immune system than did mice infected with the low inoculum. Concerning the activation of the immune system, the main findings for high-dose-infected mice were (i) increased numbers of splenocytes, with preferential expansion of CD8(+) and B220(-) CD5(-) cells, many of them bearing a macrophage phenotype; (ii) higher frequencies of B (B220(+)), CD4(+), and CD8(+) large lymphocytes; (iii) a shift of CD4(+) cells towards a CD45RBLow phenotype; (iv) increased frequencies of both CD45RBLow and CD45RBHigh large CD4(+) cells; (v) augmented numbers of total immunoglobulin (Ig)-secreting cells, with predominance of IgG2a-producing cells; and (vi) increased production of gamma interferon and interleukin 4. In addition, these mice presented lower IgM and higher IgG2a and IgG1 parasite-specific serum antibody levels. Our results indicate that the parasite load at the acute phase of T. cruzi infection influences the activation of the immune system and development of Chagas' disease pathology at the late chronic phase of the disease.