Description:
<jats:title>Abstract</jats:title>
<jats:p>The nature of the antigen determines the type of T-cell response and thereby the course of the resulting immune reaction. Especially, the binding affinity of the peptide-MHCII complex to the T-cell receptor and the presence of cytokines are crucial. In addition, it has been reported that the antigen dose used for immunization regulates T-cell fate. For example, intravenous priming with sheep red blood cells (SRBC) induces two functionally distinct T-cell populations. A high dose (10e9 SRBC) induces T cells that provide B cell help (Th2 cells) whereas a low dose (10e5) induces T helper cells that mediate delayed type hypersensitivity reaction in the skin (Th1 cells). The mechanism behind the induction of Th1 or Th2 cells is not well understood. In this study, we investigated the expression of Th1 and Th2 cytokines in the compartments of the spleen in vivo using laser microdissection and real-time RT-PCR to understand how these distinct T-cell populations are formed. Our results show that cytokine producing effector T cells appear in the spleen only after high dose priming and only in the presence of activated B cells. In contrast, T cells induced by a low dose do not start to produce cytokines in the spleen but after encounter SRBC in the skin. We conclude that the induction of cytokine producing effector T cells requires a second contact between T cells and SRBC, which is given by B cells in the spleen after high dose priming and in the skin after low dose priming.</jats:p>