Improved thymic function in exclusively breastfed infants is associated with higher interleukin 7 concentrations in their mothers' breast milk.
BACKGROUND
In rural Gambians, the season of birth strongly predicts adult mortality. Those born during the harvest season have longer life spans than do those born during the hungry season, and the deaths associated with infectious diseases suggest permanent early-life influences on immunity. Thymic measurements showed significantly smaller thymuses in infants born during the hungry season than in those born during the harvest season. The differences were greatest at 8 wk of age, a time when all infants were exclusively breastfed, which suggests the involvement of breast milk factors.


OBJECTIVE
This study tested whether thymic size differences reflect thymic output and ascertained whether thymic output is associated with breast milk interleukin 7 (IL-7) concentrations.


METHODS
We studied thymic size and output in a prospective cohort of 138 Gambian infants born in either the hungry or the harvest season by measuring signal-joint T cell receptor-rearrangement excision circles (sjTRECs) at birth and at 8 wk of age. IL-7 concentrations in breast milk were measured by using an enzyme-linked immunosorbent assay.


RESULTS
By age 8 wk, those born in the hungry season had significantly lower sjTREC counts than did those born in the harvest season (0.97 and 2.12 sjTRECs/100 T cells, respectively; P = 0.006). At 1 wk postpartum, the breast milk of mothers of infants born in the hungry season had significantly lower IL-7 than did that of mothers of infants born in the harvest season (79 and 100 pg/mL, respectively; P = 0.02). The findings were similar at 8 wk postpartum.


CONCLUSIONS
These data show a plausible pathway linking external seasonal insults to mothers with thymic development in their infants, which suggests possible implications for long-term programming of immunity.
Department of Immunology, Imperial College London, Chelsea & Westminster Hospital, 369 Fulham Road, London SW10 9NH, UK.
Pa T
PT
Ngom
Andrew C
AC
Collinson
Jeffrey
J
Pido-Lopez
Sian M
SM
Henson
Andrew M
AM
Prentice
Richard
R
Aspinall
D001942:Breast Feeding; D015331:Cohort Studies; D004797:Enzyme-Linked Immunosorbent Assay / Q000379:methods; D005260:Female; D005434:Flow Cytometry; D005714:Gambia; D006801:Humans; D007223:Infant; D007226:Infant Mortality; D007231:Infant, Newborn; D015851:Interleukin-7 / Q000032:analysis*; D018655:Lymphocyte Count; D039382:Maternal Nutritional Physiological Phenomena / Q000502:physiology; D008895:Milk, Human / Q000276:immunology*; D011159:Population Surveillance; D011446:Prospective Studies; D012424:Rural Population; D012621:Seasons; D013950:Thymus Gland / Q000033:anatomy & histology / Q000502:physiology*
D015851:Interleukin-7