The cellular immune response in the tracheal mucosa to Mycoplasma gallisepticum in vaccinated and unvaccinated chickens in the acute and chronic stages of disease

Mycoplasma gallisepticum causes a lymphoproliferative response in the tracheal mucosa of infected birds. The studies reported here aimed to determine, using immunohistochemical and immunofluorescent staining, which lymphocyte subsets were infiltrating the mucosa during the acute and chronic phases of disease and to determine whether these subsets differed in birds that had been vaccinated with strain ts-11. In vaccinates there was no detectable infiltration of T or B lymphocytes between 1 and 6 weeks after infection with a virulent strain. Unvaccinated birds had an initial influx of CD8+TCR− lymphocytes at 1 week, with the numbers decreasing over the next 5 weeks. CD8+TCR+ cells increased over the 6 weeks. The proportion of CD4+TCRαβ2+ cells also increased, whilst there was an increase in CD4+TCRαβ1+ cells at 3 weeks and then a decrease by 6 weeks. B lymphocytes were not detected until 3 weeks after infection, and their appearance coincided with a decrease in the concentration of mycoplasma DNA detectable in the trachea. The formation of clusters of CD8+TCR− lymphocytes was a prominent feature of the early response, while at 3 and 6 weeks after infection clusters of B cells became prominent, although in some cases they surrounded a cluster of CD8+ cells. These observations suggest a primary role for local antibody mediated responses in controlling M. gallisepticum infection, but also show that there are probably significant natural killer and cytotoxic T cell responses to infection, although the efficacy of these in controlling infection was not able to be determined.