Secretory immune responses to Mycoplasma pulmonis

Formalinized Mycoplasma pulmonis, along with aluminum hydroxide as an adjuvant, was used to subcutaneously immunize rats in the vicinity of the salivary gland to examine the characteristics of the secretory immune response to this pathogen. The induction of specific antibody to this microorganism was detected in serum and the exocrine fluids, namely, saliva and lung lavage fluid. Both immunoglobulin G (IgG) and IgA isotype antibodies were detected in each of these fluids after primary and secondary local immunizations. Serum responses from immunized animals were significantly greater than in the control group, but a dose response was not observed in either IgG or IgA antibody at the dosages selected for immunization. Salivary IgG antibody responses peaked early after both the primary and secondary immunizations, exhibiting a clear dose response. Salivary IgA in immunized groups was significantly greater than that in the control group but displayed little dose-dependent kinetics, and, at the termination of the experiment, this response had not yet peaked. Lung lavage IgG and IgA were minimal after the primary immunization when the antibody was normalized to total protein but displayed dose-dependent kinetics after a secondary challenge. IgG peaked immediately after a secondary challenge, while IgA peak responses were observed only after 20 days. A positive correlation was noted between the serum, saliva, and lung lavage fluid IgGs after both primary and secondary immunizations and only after a secondary challenge for IgA. In this study we were able to elicit a secretory immune response, consisting of both IgG and IgA, which exhibited a dose-dependent characteristic in lung lavage fluid to this immunogen. Additionally, a positive correlation of antibody levels between saliva and lung lavage fluid suggests that saliva could be used as an indicator for monitoring specific antibody to M. pulmonis in lung lavage secretions without requiring invasive, deleterious procedures.