Both age and gender affect thymic output: more recent thymic migrants in females than males as they age

The thymus undergoes age-associated involution, with studies showing thymic size decreasing from birth at a rate of approximately 3% per year until mi ddle age, and at a rate of 1% per year thereafter. The aim of this study wa s to determine the effect of thymic atrophy on T-lymphocyte production by t he thymus, and to clarify the ongoing uncertainty regarding gender differen ces in thymic function. We quantified recent thymic emigrants (RTEs) in blo od through the measurement of signal joint T-cell receptor rearrangement ex cision circles (sjTRECs), and showed that the decline in the number of RTEs in the blood with increasing age is gender-linked. Peripheral blood from f emales contained significantly higher levels of sjTRECs per CD3(+) T cell t han blood from males (P = 0.002), despite there being no significant gender difference in the absolute number of CD3(+) T cells in the populations ana lysed (P > 0.10). Our findings suggest better thymic function in females co mpared with males, providing females with a higher number of recent thymic emigrants for longer periods of life. Such a finding provides a plausible e xplanation for the immunological gender differences observed in previous st udies and possibly, for the general longer life expectancy in females compa red with males.