Nematode infection induces Th2 cell-associated immune responses in LEC mutant rats with helper T cell immunodeficiency.

Long-Evans Cinnamon (LEC) rats have maturational arrest of CD4+8- T cells from CD4+8+ cells in the thymus. Despite this, CD4+8- T cells are always present in peripheral lymphoid organs of LEC rats, suggesting that these CD4+8- T cells are generated by an uncommon pathway. We investigated the role of LEC rat peripheral CD4+8- T cells in Th2-associated responses to infection with the nematode Nippostrongylus brasiliensis. After infection, the numbers of CD4+8- TCR alpha beta + T cells significantly increased in mesenteric lymph nodes (MLN) and the spleen, while those in the thymus were still negligible. Infection also induced significant up-regulation of IL-4 gene expression in LEC rat MLN cells. Total serum IgE levels in LEC rats were markedly increased two weeks after infection. Mucosal mast cell responses in the gut and lungs of LEC rats were induced as prominently as in control Long-Evans Agouti (LEA) rats. Faecal egg count data indicated that LEC rats rejected nematodes faster than LEA rats. These results suggested that Th2-associated responses can be induced by nematode infection in LEC rats probably through the extrathymic recruitment and proliferation of CD4+8- TCR alpha beta + T cells.