Detection of an IgM antiglobulin in the sera of atopic patients using insolubilized IgG4, and its capacity to release histamine from leucocytes.

ELISA plates coated with highly pure IgG4 were employed to detect IgM antiglobulin in atopic sera. The use of IgG4, rather than whole IgG, on the solid-phase was to provide direct evidence for the IgG4 reactivity of the antiglobulin. Bound IgM was shown to be antiglobulin in that binding can be inhibited by pre-absorption of serum with IgG. Some 75% of asthmatic patients and 29% of eczema patients were found to have significantly raised level of IgM antiglobulin. This antiglobulin resembles rheumatoid factor in that it appears to be directed against antigenic determinants common to human and rabbit IgG. Isolated antiglobulin-enriched IgM fractions released histamine from leucocytes of 7 out of 12 atopic patients. The histamine-releasing capacity of the IgM antiglobulin was shown to be operating via basophil-bound IgG in that the process can be blocked by pre-absorption of the antiglobulin with IgG. Furthermore, heating the antiglobulin-enriched IgM fraction did not affect its histamine-releasing capacity. We conclude that the IgM antiglobulin detectable in our atopic patients may contribute to the pathological changes in them.