Immunomodulatory properties of Mycoplasma pulmonis. I. Characterization of the immunomodulatory activity.

For many years, it has been recognized that Mycoplasma infection affects the host's immune system in different ways. In this work, experiments were performed to characterize the influence of Mycoplasma pulmonis infection on various immunological parameters and to follow the kinetics of their variations. A Balb/c mouse model was used to assess hematological evaluations, changes in spleen weight, antibody responses against sheep erythrocytes, neutrophil phagocytosis, colloidal carbon clearance, and anti-Mycoplasma antibody responses. At the hematological level, infected animals were found to have significantly increased total lymphocyte and polymorphonuclear leukocyte counts and an augmentation in spleen weight. Seven days after Mycoplasma infection, antibody responses against sheep erythrocytes were considerably diminished, and at days 7 and 14 after infection, phagocytic activity was also reduced. After 1 week of infection, the colloidal carbon clearance pattern was decreased, and during the whole infectious process, anti-Mycoplasma antibody titers were found to be low. Results from this part of research show a persistent infection that does not resolve in a short period, which is associated with a general dysfunction in the immune system and poor immune responses against several different antigens.

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-gamma and IL-4 were detected in sera, such that at day 15, there was a peak in IFN-gamma, concentration and at day 38, IL-4 concentration also peaked. By day 46, both IFN-gamma 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.