Measles infection. Involvement of the complement system.

The complement system was examined in fifty patients with acute, apparently uncomplicated measles; forty-six were children less than 10 years old. Twenty showed evidence of pathological complement activation. In thirteen of these the pattern was consistent with activation of the classical pathway while in the other seven data suggested utilization of an alternative pathway. An additional eleven patients had isolated reduction in Clq without alteration in concentration of other components; these were excluded from the classical pathway group. No patient had detectable immune complexes or C3 splitting activity in serum; however, it is suggested that the abnormal complement patterns observed are likely to indicate the presence of circulating immune complexes in a high percentage of patients with this infection.