Cold‐reactive rheumatoid factors in infectious mononucleosis and other diseases

A high percentage of patients with infectious mononucleosis showed in their sera a special type of rheumatoid factor that reacts at 4°C but not at 22°C with cells or other particles coated with γ globulin. This differed from the usual types of rheumatoid factor found in the sera of patients with rheumatoid arthritis, where no such temperature dependence was evident. The potentiation of the Rh agglutination test at 4°C provided a sensitive method for the detection of this unusual rheumatoid factor. Similar cold‐reactive rheumatoid factors were also found in the sera of patients with reticulum cell sarcoma and certain other disorders. They precipitated with γ globulin in the cold and resembled the well‐known γM‐γG mixed cryoglobulins. Whether routine screening tests for rheumatoid factor will or will not detect these cold‐reactive rheumatoid factors depends upon the temperature at which the tests are performed.