Avian coccidiosis. A review of acquired intestinal immunity and vaccination strategies

The gut-associated lymphoid tissues contain B and T lymphocytes responsible for acquired immunity to avian coccidiosis. Intestinal B cells begin produ cing parasite-specific antibodies shortly after infection although their ro le in protecting against coccidiosis is debated. T-cell-mediated immunity, predominantly by intestinal intraepithelial lymphocytes and lamina propria lymphocytes, confers the main component of protective immunity to Eimeria. Many of these cells display the CD8 and gamma delta T-cell receptor surface antigens, phenotypic markers of cytotoxic T cells. Although their role in eliminating Eimeria infection remains to be completely elucidated, T cells have been implicated in parasite transport, and their activity is augmented by interferon-gamma and interleukin-2. Because of the importance of cell-m ediated immunity, coccidiosis vaccines must be capable of stimulating intes tinal T cells. Orally delivered, live parasite vaccines, either unattenuate d or attenuated, are powerful stimulators of intestinal cell-mediated immun ity, but antigenic variability between Eimeria species present in the vacci ne and in the field may restrict their commercial application. The newer ge nerations of recombinant DNA and subunit protein vaccines, particularly whe n used in conjunction with interferon-gamma and interleukin-2, have shown p reliminary promise in controlling experimental infections but have yet to b e commercially developed.