The thymus in pregnancy: the interplay of neural, endocrine and immune influences

This article discusses the dramatic events that accompany thymic involution during pregnancy, and traces the possible immune, neural and endocrine interactions that may occur. Ann Clarke and Marion Kendall present accumulating evidence that activity, not inactivity, is a feature of the thymus at this time. Whilst the cortex shrinks, the medulla enlarges and rearranges to create a microenvironment containing increased numbers of mature thymocytes. It is suggested that these recently derived T cells may contribute to the unique populations of cells with suppressive function that appear during pregnancy, and thereby contribute to the immune suppression of the mother to paternal and fetal antigens. In addition, the pregnancy-associated cortical involution of the thymus may reflect the deletion of clones with potential reactivity to paternal and/or fetal antigens.