Pregnancies modulate B lymphopoiesis and myelopoiesis during murine ageing

We recently reported that pregnancy affects age-related changes in the dist ribution of lymphoid and macrophage populations in the spleen of C57B1/6 mi ce. Tn the present study, we examined the influence of pregnancies on the g eneration of various developmental B-cell subsets and granulocyte/macrophag e lineage cells during murine ageing. Using flow cytometry, changes in lymp hoid (mature and early B-cell precursors: B220(high), E220(low), surface im munoglobulin M (sIgM) mu chain +/-) and myeloid (monocyte/macrophage Mac-1/ CD11b, granulocyte Gr-1/Ly-6G) compartments were monitored in the bone marr ow of young (2 months) and 15- and 23-month-old mice including male, multip arous and virgin female mice, pregnancies delayed the age-related decline i n murine B lymphopoiesis and maintained B-cell reserve capacity during agei ng. We also found an increased production of myeloid cells induced by pregn ancies at middle (15 months) and advanced (23 months) ages. This comparativ e study provides new information on changes in marrow lymphopoiesis and mye lopoiesis with age. Our data emphasizes that the onset, magnitude and kinet ics of age-related changes in the haematopoietic marrow are parity dependen t. These changes could influence the incidence of age-related diseases and may account for the greater longevity of females.