The responsiveness of various maternal mouse lymphocyte populations to mitogenic stimulation in vitro

Abstract

Lymphocytes from various lymphoid organs in age matched pregnant, postpartum and virgin Swiss mice were stimulated in vitro with the mitogens phytohaemagglutinin (PHA), concanavalin A (Con A), and Escherichia coli lipopolysaccharide (LPS). Most lymph node and spleen lymphocyte cultures from pregnant animals were slightly less responsive to mitogenic stimulation than comparable cultures from nonpregnant animals. However, in pregnant animals no difference was found between the responsiveness of lymphocytes from lymph nodes that drained the fetal implantation site and the responsiveness of lymphocytes from sites distal to the uterus. Thus, the pregnant mouse is slightly systemically immunosuppressed, but fetal products such as placental hormones apparently do not exert a local immunosuppressive effect detectable in the regional lymph nodes. A marked pregnancy-associated alteration in immunological responsiveness was found in maternal thymus cell cultures. A four- to sixfold increase in the PHA responsiveness of thymocytes taken from animals during late pregnancy or immediately after parturition was observed. This increase in PHA responsiveness was associated with marked atrophy of the maternal thymus. Because the thymus is the primary lymphoid organ influencing the development of T lymphocytes that mediate cellular immunity and help regulate humoral immunity, such changes in the maternal thymus could reflect basic changes in the maternal immune system that occur in the accommodation of the antigenically foreign fetus.