CTSL from fibroblastic reticular lymph node cells negatively regulates conversion of CD4 cells to the Treg cell phenotype

MAGLIOCO ANDREA; CAMICIA GABRIELA; N BADANO; COSTA HéCTOR; CAMERANO GABRIELA; PIAZZON ISABEL; NEPOMNASCHY IRENE

Mar del Plata

Congreso; LIX Reunión Científica Anual de la Sociedad Argentina de Investigación Clínica (SAIC). LXII Reunión Científica Anual de la Sociedad Argentina de Inmunología (SAI); 2014

SAIC-SAI

Cathepsin L (CTSL) is a lysosomal cysteine peptidase with diverse and highly specific functions. We and others have shown that CTSL is involved in thymic CD4+ T-cell positive selection. Using CTSL nkt/nkt mice that lack CTSL activity we have previously demonstrated that the absence of CTSL activity correlates with increases both in the number of lymph node (LN) and spleen CD4+CD25+Foxp3+ (Treg) cells and in the ratio between CD4+ Treg and CD4+CD25-Foxp3- (T conv) cells within CD4+ cells. Contrarily, CTSL nkt/nkt and wt mice show no differences both in the number of thymic CD4+CD8- Foxp3+ cells or in the ratio between Treg and Tconv cells within CD4+CD8- thymocytes, suggesting that the increase in the number of LN Treg cells is established in the periphery of mutant mice. Herein we analyzed whether conversion is involved in the increase in the Treg peripheral cell number in CTSL nkt/nkt mice and the involvement of LN stromal cells (LNSC). LN CD4+CD25-Foxp3-cells activated with anti-CD3, anti-CD28 and IL-2 but without exogenous TGF-β1 were cultivated with supernatants (sn) from mutant or wt LNSC. Conversion was significantly increased by the addition of mutant vs wt LNSCsn (i.e. percentage of Treg cells in CTSL nkt/nkt Tconv cells cultured with mutant or wt LNSCsn: 15.8+2 vs 7.3+1.2, n=3,p0.01, n=3; measured by ELISA). More than 97% of both mutant and wt LN stromal cell lines were gp38 + CD35- CD21-, indicating a fibroblastic reticular phenotype. These results indicate that conversion can play a role in the increase of Treg cells in the periphery of CTSL nkt/nkt mice, being TGF-β production by fibroblastic reticular LN stromal cells involved. Moreover, they suggest that CTSL is able to negatively regulate the conversion to Treg cells in non immunoprivileged sites.