PREGNANCY, IMMUNOSUPPRESSION AND REACTIVATION OF LATENT TOXOPLASMOSIS

Toxoplasmosis is a chronic, latent infection which can be reactivated in the presence of immunosuppression. The critical question in obstetr ics is whether toxoplasmosis may be reactivated in the presence of the physiological ''immunosuppression'' of pregnancy. Standard in vitro t ests, done in 24 healthy pregnant women and compared with the literatu re, show no significant changes in humoral and cellular immunity durin g pregnancy. However, the fact that some infections occur more frequen tly and more severely than in non-pregnant women (e. g. those due to c ytomegalovirus (CMV) and human papilloma virus (HPV) points to a degre e of pregnancy-associated immunosuppression. Non-rejection of the semi allogenic fetus is achieved in presence of maternal immunocompetence a nd is explained mainly by local changes in immune function, mediated b y inhibitors of decidual, placental and fetal origin, and by the absen ce of class II histocompatibility antigens at the fetomaternal interfa ce. Immune status allowing reactivation of toxoplasmosis was studied i n a selected group of(predominantly male) AIDS patients from the Swiss HIV Cohort study. Shortly before (cerebral) reactivation of toxoplasm osis, 92% of these patients had very low CD4 lymphocyte counts (mean 5 0 cells/mu l, i. e. lower than ever recorded in a normal uncomplicated pregnancy). In a larger population of 48 women receiving immunosuppre ssive therapy after organ transplantation, not a single case of cerebr al toxoplasmosis was observed during pregnancy, while in the 105 HIV-p ositive women in the Swiss HIV and Pregnancy study, there was only one case of cerebral toxoplasmosis during pregnancy and the puerperium (2 0 CD4/mu l), even though some 17% of those sampled (18/105) had CD4 le vels below 200 cells/mu l on at least one occasion during pregnancy. T hese findings explain why latent toxoplasmosis is not reactivated in n ormal pregnancy, and why it is only likely in an immunosuppressed moth er when her CD4 lymphocyte count is very low (< 200 cells/mu l). In su ch cases, a prophylactic treatment to prevent maternal reactivation an d vertical transmission of toxoplasmosis may be useful.