Protection from Cryptosporidium parvum infection by gammadelta T cells in mice that lack alphabeta T cells.

BACKGROUND AND PURPOSE: Cryptosporidium parvum establishes a parasitic relationship with epithelial cells of the intestine. Infection with this protozoan is resolved in the immunocompetent host, but persistent life-threatening infection develops in the immunocompromised host. We propose that gammdelta T cells in the intestinal mucosa play a role in immunity to C. parvum.

METHODS

Intestinal intra-epithelial lymphocyte and lamina propria T-cell subsets were examined in mice infected with C. parvum. The mice are homozygous for a deletion of the TCRalpha chain gene, TCRalpha(-/-) and, therefore, lack conventional alphabeta T cells, but retain a population of T cells with gammadelta T-cell receptors. To examine the contribution of gammadelta T cells to immunity, these mice were treated with monoclonal antibody GL3-3A, specific for this T-cell receptor, then were inoculated with C. parvum oocysts. Lymphocyte subsets and hematoxylin and eosin (H&E)-stained intestinal sections from untreated mice were compared with those from mice treated with either a low dose of GL3-3A for 6 weeks, or a high dose of GL3-3A for 16 weeks.

RESULTS

The proportion of gammadelta T cells in the lamina propria increased in infected mice. In mice treated with a low dose of GL3-3A, a population of gammadelta T cells that had characteristics of activated cells, was still evident 6 weeks after inoculation. No C. parvum developmental forms were identified in the intestinal sections of mice under these conditions. However, TCRalpha(-/-) mice treated with a high dose of GL3-3A were depleted of gammadelta T cells, and 50% of the mice were infected with C. parvum.

CONCLUSIONS

The gammadelta T cells contribute to protection against C. parvum infection. In the absence of conventional T cells, activation of intestinal gammadelta T cells may prevent infection with this organism.