Response of T Lymphocytes From Previously Infected Calves to Recombinant Cryptosporidium parvum P23 Vaccine Antigen

We had previously demonstrated that a Type-1-like immune response involving interferon-γ expression in lamina propria lymphocytes accompanied by IgG₂ subclass fecal antibodies to Cryptosporidium parvum p23 emerged in gut mucosa of calves recovering from cryptosporidiosis. Because a recombinant p23 had been shown to protect calves from cryptosporidiosis when administered as a vaccine antigen to late gestation cattle, this study was undertaken to determine if the same vaccine antigen could induce a Type-1-like, in vitro response by T cells from calves that had recovered from C. parvum infection. We isolated peripheral blood mononuclear cells from calves that had been previously infected with C. parvum oocysts and incubated them in the presence or absence of the recombinant C. parvum p23 vaccine antigen. We used flow cytometry to simultaneously detect cells in cell cycle and identify the T cell subset containing cycling cells. We also used flow cytometry to identify interferon-γ positive cells and 2-dimensional gel electrophoresis to profile proteins made by PBMC stimulated with the recombinant p23 vaccine antigen. The results demonstrated that CD4⁺ T lymphocytes proliferated and that interferon-γ was synthesized by a subset of stimulated cells. Two-dimensional gel electrophoresis revealed the presence of several cytoplasmic proteins in a size range of approximately 25–80 kDa that were detected in p23-stimulated, but not in unstimulated, cytoplasmic samples. Together, the results show that the recombinant p23 vaccine antigen can stimulate a Type-1-like immune response by T cells from calves that have recovered from C. parvum infection.