Effect of surface antigen-1 (SA-1) immune lymphocyte subsets and naive cell subsets in protecting scid mice from initial and persistent infection with Cryptosporidium parvum.

We tested the hypothesis that adoptive transfer of immune spleen cell subsets from Cryptosporidium parvum antigen immunized, immunocompetent BALB/c mice would prevent initial infection or terminate persistent infection in severe combined immunodeficient (scid) mice. Cell donor mice were immunized with either solubilized C. parvum oocysts and sporozoites (positive control) or a surface antigen-1 (SA-1) enriched C. parvum antigen fraction. Both groups of BALB/c cell donor mice immunized with C. parvum antigens had increased antibody titers and lymphoproliferative responses when compared with negative control mice injected with phosphate buffered saline and adjuvant. Intravenous adoptive transfer of 5 x 10(6) cells of each cell subset (spleen cells, CD4 T and B lymphocytes, CD4 T lymphocytes or B lymphocytes) derived from immunized adult BALB/c donor mice did not protect scid mice against initial infection of the gastrointestinal epithelium with C. parvum, despite flow cytometric evidence of CD4 T lymphocyte engraftment in the spleen and detectable levels of C. parvum-specific serum antibody. In contrast, intravenous injection of either naive or immune CD4 T and B lymphocytes combined, or CD4 T lymphocytes alone, terminated persistent C. parvum infection in scid mice. Intestinal infectivity scores were significantly reduced by 9 days post-engraftment in all groups and continued to decline throughout the remainder of the experiment. Flow cytometric analysis demonstrated significantly increased CD4 T lymphocytes in the spleens of recipient scid mice when compared with infected scid mice receiving no cells. Cryptosporidium parvum-specific antibody was detected on day 12 post engraftment in mice receiving SA-1 immune CD4 T and B lymphocytes but was not detectable in mice receiving naive cell subsets.