Immunomodulatory properties of Mycoplasma pulmonis: II. Studies on the mechanisms of immunomodulation

Mycoplasma infection affects the host's immune system in different ways. In this work, a kinetic approach was used to try to determine the mechanisms by which Mycoplasma cause these effects. Experiments were performed using Balb/c mice infected with Mycoplasma pulmonis and several immunological parameters were determined. It was found that at days 10 and 15 post-infection, there were significant changes in the percentages of CD4+ and CD8+ cells, in both peripheral blood and the thymus. Significant sequential increases in concentrations of both IFN-γ and IL-4 were detected in sera, such that at day 15, there was a peak in IFN-γ concentration and at day 38, IL-4 concentration also peaked. By day 46, both IFN-γ and IL-4 fell to control levels despite continued infection. Delayed hypersensitivity (DTH) was reduced in infected animals compared to non-infected controls. A small recovery in DTH was observed at day 30, which was reduced again by day 40. Altogether, the results show features of a transitional shift from Th₁ to Th₂ in animals that are ultimately immunologically incompetent (in both cellular and humoral immunity). It appears to be this state of incompetence that allows the microorganism to survive and thus provides an explanation for the chronic state of the disease, which is a characteristic of Mycoplasma infection.