The influence of social rank on the susceptibility of rats to Mycoplasma arthritidis.

Social ranks (A, O, rest) of adult male inbred rats housed in groups of four per cage were determined by repeated observations of their ejaculatory patterns under competitive conditions. Once ranked, they were intravenously infected. Fifteen clinical, hematological, and serological characters were continuously observed during 110 days. Body weight reduction, arthritis score, and specific IgG antibody titers were chosen as guideline characteristics and compared between different genotypes and social rank classes. Genotypic differences account for 60-80% of the individual differences and social rank differences account for 0-40% of the individual differences within isogenic animals. Social rank affects the individual genotypes in an opposite way. Rank A males are less susceptible in genotype DA but showed increased susceptibility in genotypes AS. In genotype LEW, influence of social rank on susceptibility to Mycoplasma arthritidis could not be verified. Specific IgG antibody titers are lower in ranks showing a higher degree of susceptibility.