a1 MRC International Nutrition Group, Nutrition and Public Health Interventions Research Unit, Department of Epidemiology and Population Health, London School of Hygiene and Tropical Medicine, Keppel Street, London, WC1E 7HT, UK
a2 MRC Keneba, MRC Laboratories, The Gambia, West Africa
a3 Directorate of Child and Women's Health, Royal Devon and Exeter Hospital (Wonford), Exeter, EX2 5DW, UK
a4 Department of Immunology, Imperial College London, Chelsea and Westminster Hospital, London, SW10 9NH, UK
In rural Gambia the risk of mainly infection-related mortality is 10-fold higher for adults born in the nutritionally-debilitating ‘hungry’ season, suggesting that immune function may be compromised by events early in life. The current programme of research focuses on the biological mechanisms underlying this hypothesis, exploring early-life environmental influences on immune development and the long-term functional consequences these influences may have. Results obtained to date show that thymus development during infancy is critically sensitive to environmental exposures, with smaller thymuses observed in the hungry season. Measurement of the frequency of T-cell receptor excision circles indicate that thymus function is also sensitive to seasonal influences, with further studies implicating variations in breast-milk IL-7 as a possible mediator of these effects. Studies in adults have shown that size at birth is positively correlated with antibody responses to vaccination with polysaccharide antigens, thus providing evidence for long-term functional deficits. The present paper will review progress made to date within this field of research.