Immunoglobulin class- and subclass-specific responses to Mycoplasma pulmonis in sera and secretions of naturally infected Sprague-Dawley female rats.

Mycoplasma pulmonis causes chronic murine respiratory mycoplasmosis and genital disease in rats. Specific immunoglobulin M (IgM), IgA, and IgG and its subclasses present in sera and tracheal and uterine lavage samples from 36 naturally infected Sprague-Dawley female rats were tested for reactivity with M. pulmonis in an enzyme-linked immunosorbent assay. Ten specific-pathogen-free Sprague-Dawley female rats served as the negative controls. Tracheal and uterine lavage samples were cultured quantitatively for M. pulmonis. M. pulmonis was isolated from the trachea (35 of 36) and uterus (17 of 36) of naturally infected rats; all rats were infected in at least one of the two sites cultured. M. pulmonis was not isolated from any control rat. There was a significant difference in levels of specific antibody of all classes except IgG2c between control and naturally infected animals (P less than 0.001 for IgM, IgG, IgG1, and IgG2a; P less than 0.002 for IgG2b; and P less than 0.02 for IgA). There was no correlation between numbers of M. pulmonis cells isolated and the amount or class of antibody measured in serum or tracheal lavage specimens. The predominant antibodies to M. pulmonis found in the sera of naturally infected rats were IgG and IgM. The IgG2a subclass was responsible for the majority of IgG-positive animals. There were no differences between rats which were positive by culture for M. pulmonis in the uterus (U+) and rats which were negative by culture for M. pulmonis in the uterus (U-) with respect to distribution or amount of antibody classes and subclasses in the serum. However, tracheal wash samples from U+ rats had significantly higher (P less than 0.03) levels of specific IgG1 and IgG2a than those from U- rats. Conversely, IgG2a was present in higher levels in pooled uterine lavage specimens from U- rats than in those from U+ rats.