Defect in TCR-CD3ζ signaling mediates T cell hypo-responsiveness in mesenteric lymph node

Mesenteric lymph node (MLN) in gut-associated lymphoid tissue plays obligatory roles in the induction of oral tolerance and ignorance to commensals. However, little is known about its immunological characteristics. In this study, we investigated the hypo-responsiveness of MLN CD4+ T cells, comparing them with spleen CD4+ T cells. MLN CD4+ T cells were hypo-proliferative and expressed low levels of Th1-type cytokines in response to antigen or CD3/T cell receptor (TCR) stimulation. The hypo-responsiveness of MLN CD4+ T cells is linked neither with changes in the regulatory T cell population (CD4+CD25+, CD4+Foxp3+) nor the apoptotic population. Rather, MLN CD4+ T cells showed deformity of T cell:APC conjugation and reduced expression of TCR signaling molecules such as CD3ζ, PLC-γ1, PKC-θ, Zap70, with reduced phosphorylation of immunoreceptor tyrosine-based activation motifs (ITAMs). Among the alterations in TCR signaling molecules, defective CD3ζ expression is the most evident, and reversal of the anergic state by CD3/CD28 costimulation restored CD3ζ expression levels. Collectively, we suggest that reduced CD3ζ expression and defects in TCR signaling mediate the anergy state of MLN CD4+ T cells, which play a critical role in maintenance of mucosal tolerance in gut-associated lymphoid tissue.