Immunoconglutinins of different immunoglobulin classes demonstrated by the antiglobulin reaction.

The development of an antiglobulin test enabled the demonstration of autoantibodies directed against fixed complement components (immunoconglutinins or IKs) of immunoglobulin classes other than IgM. All human and rabbit sera tested had IgG IK activity. The titres, though variable, were usually comparable with those of the IgM variety. Rabbit IgG IK was stimulated by the autostimulation methods used in the past for IK (IgM) production and had a similar reactivity, being mainly directed against C′. IgA IK was detected in three of the human sera, and both IgG and IgA IK from one of these were shown to be autoreactive.