The isotype and specificity of antiglobulins in BALB/c mice.

Antiglobulin activity was detected in the IgM class and the IgG1, IgG2a and IgG2b subclasses in normal and unstimulated BALB/c mice. There was an age related increase in their IgM antiglobulin, but this increase was not observed with IgG antiglobulin. Antiglobulin production could be induced by polyclonal activation of BALB/c mice with lipopolysaccharide, but this produces an increase in IgM antiglobulin only. IgM antiglobulin binding with mouse IgG1 and human IgG peaked on day 4 following lipopolysaccharide, whereas IgM antiglobulin binding with mouse IgG2a peaked around day 7. There was no IgM response with specificity for binding to mouse IgG2b. The level of IgG antiglobulin remained constant following polyclonal activation of BALB/c mice with lipopolysaccharide. Interestingly IgG antiglobulin binds preferentially with isologous IgG compared with heterologous IgG. Possible physiological roles have been discussed for the presence of these rheumatoid factors in normal mice.