American Journal of Clinical Nutrition, Vol 27, 908-915, Copyright © 1974 by The American Society for Clinical Nutrition, Inc.

Interrelationships between dietary protein, immunoglobulin levels, humoral immune responses, and growth in New Guinean schoolchildren

¹ From the Clinical Research Unit, Walter and Eliza Hall Institute, Royal Melbourne Hospital, 3050, Victoria, Australia

A daily dietary supplement of 25 g protein (as skim milk powder) was fed to a group of 30 growth-retarded prepubertal children attending the boarding school in Bundi, New Guinea. A control group of 24 growth-retarded children received only the normal school diet. At 7 months, all children were immunized with flagellin from Salmonella adelaide; specific antibody responses were measured over the ensuing 6 weeks and total immunoglobulin levels were also measured. Growth was assessed at 8 months. Increments in height and weight and antibody responses to flagellin were significantly greater in children receiving the skim milk supplement than in those receiving the normal school diet whereas levels of total immunoglobulin M were higher in the latter than in the former. Factor analysis showed that natural (preimmunization) antibody to flagellin was correlated with total IgM levels but was largely independent of postimmunization antibody levels and of total levels IgA and IgG. Active production of antibody to flagellin was independent of total levels of IgG, IgA, and IM. These findings are of theoretical interest; first, they suggest that the causes of specific antibody production after immunization are largely independent, not only of those for "natural" (preimmunization) antibody, but also those for total immunoglobulin levels. In view of the fact that the children receiving a dietary supplement had lower immunoglobulin levels in spite of their higher antibody responses, it is suggested that inadequate dietary protein impairs the production of specific antibody molecules, and that by way of compensation, there is a greater production of immunoglobulin molecules of low antibody specificity that are less effective in eliminating infectious agents. From a practical viewpoint, these results suggest that modest increases in protein intake would benefit the health status of people in the developing countries. In contrast, it is possible that, in the developed countries, overnutrition might modify immune function in a way that is harmful to health.