A complex balance between the detrimental and beneficial effects of immunity determines the course of mycoplasma respiratory infection. NK cells were shown to dampen innate immunity in the lungs. The purpose of this study was to determine if NK cells similarly impacted the development of adaptive immunity against mycoplasma disease. Anti-asialoGM1 Ab was used to transiently deplete NK cells prior to nasal-pulmonary immunization with mycoplasma membrane Ag. Unimmunized and mice receiving only anti-asialoGM1 Ab served as controls. The treatment was repeated 7d later and the mice were challenged on day 14 with M. pulmonis. DX5+ NK cell numbers returned to normal by day 14. Colony forming units (CFUs) in lungs and nasal passages were determined 3, 7 and 14d later.
There was a significant decrease (>1 log) in CFUs in the NK cell depleted, immunized mice as compared to immunized or control mice. No such effect was seen in SCID mice, indicating adaptive immunity was affected. Further support that the protection rendered due to depletion of NK cells prior to immunization, was lymphocyte-mediated, was demonstrated when protection was shown to be adoptively transferred to naïve mice using total lung lymphocytes, purified T and/or Non T cells.
In conclusion, NK cells dampen the generation of protective adaptive immunity associated with nasal-pulmonary immunization, and this effect is on the generation of lymphoid cell mediated response. These results should provide insights into approaches to generate optimal protective immunity against mycoplasma respiratory diseases.