Immunity to and infant mortality from measles.

The age-related sequential immune response to natural measles was investigated in order to establish the role of immunodeficiency in the high infant mortality from infectious diseases. There was no difference in lymphocyte transformation, complement-fixing antibody titres, serum IgG, IgM, IgA, C3 and factor B levels, total haemolytic complement and the alternative pathway of complement over a 6-week period after onset of the rash in those younger than 12 months (group A) compared with children older than 12 months (group B). The absolute number of peripheral blood lymphocytes, comprising T, B and null cells, was higher on different days in group A compared with group B. Throughout the 6 weeks group A had higher haemagglutination inhibition antibody levels and lower serum C4 levels than Group B. The inhibition of leucocyte migration to measles antigen was similar in the two groups, except on day 28 when it was significantly higher in group B. There were 5 deaths, all in infants younger than 15 months of age. Most immunological reactions studied were not age-dependent, while those differences detected in the younger age group involved factors known to indicate a good prognosis. Therefore, the high mortality rate reported for measles in infants is unlikely to be due to immunodeficiency in this age group.