Complement and immunoglobulin levels in early childhood in homozygous sickle cell disease.

Complement levels, tests of complement function, and immunoglobulin levels were studied in 63 children with homozygous sickle cell (SS) disease and in 88 children with a normal haemoglobin (AA) genotype from birth to 2 yr of age. Levels of complement component C3 were consistently lower in SS children, the difference being highly significant (p less than 0.001) by the age of 2 yr and levels of C3d were significantly higher from the age of 6 months. These observations are compatible with increased turnover of C3 in SS disease from early in life. No consistent genotype differences were observed in the levels of C4, factor B, or functional assays. IgA levels in SS disease were significantly higher at age 2 yr but there were no consistent patterns with IgM or IgG. There was no difference in the prevalence of infections between groups with low C3 or low values of alternative pathway activity but the groups were small and only capable of detecting major differences. However, the findings cast some doubt on the role of individual complement deficiencies in the susceptibility to infection in SS children at this age.