[Effect of the amniotic fluid on the formation of spontaneous rosettes].

Since half of the fetal transplantation antigens are paternal in origen, the conceptus could be considered as a particular allogeneic graft not rejected by the mother. The reason for this particular kind of tolerance remains mostly unknown, and an enormous amount of experimental work, clinical observations and hypothesis, sometimes contradictory, has been accumulating in the scientific literature. So far no one has been able to set an unifying and coherent explanation. Recently Gupta and associates suggested that the amniotic fluid (A.F.) could have an immunosuppressive effect and protect the conceptus from the attack mediated by the mother's immunocompetent system. The basis for this approach is in a previous work made by Murgita and Tomasi in mice. These authors showed that the mouse A.F. has inhibitory effect on its T cells, and this action was well correlated with the alpha-fetopretein content in the A.F. Gupta studied A.F. from five normal human pregnancies and incubated it with lymphocytes obtained from healthy volunteers. These cells showed a clear decrease in its rosette forming abilities. Extrapolating from the Murgita and Tomasi work, conclusions were arrived at that the alpha-fetoprotein present in human A.F. was responsible for the inhibitory effect. We have obtained 23 human A.F. from non pathological, a term pregnancies, and studied its action upon rosette formation. Two populations of spontaneous rosette forming T cells could be assayed: those binding sheep red blood cells (SRBC) at room temperature (active rosettes), and those needing incubation for two hours at 4 degree C. These two populations differ on its affinity for the SRBC, being the "active" ones those probably involved in the effector arm of the specific cellular immunity. The A.F. were obtained by amniocentesis or transvaginal methods, and those grossly contaminated by erythrocytes were discarded. After centrifugation and Millipore filtering, pH and osmolarities were recorded. Blood obtained from healthy donors was centrifugated on Ficoll-Hypaque and the mononucleated cell layer washed twice and incubated with latex particles 0,81 mu diameter, in order to exclude those with phagocytosing properties on the final score. Aliquots of the cells were incubated in A.F. or Hanks balanced salt solution 30' at 37 degree C. After centrifugation the supernate was discarded, and the cell pellet resuspended in Hanks. The "active" rosette test was made according to Wybran, and the "late" test as described by Ross. A rosette was defined as a mononucleated cell without engulfed latex and with three or more SRBC binding on its surface. The mean percentage of total rosettes was 51.4 +/- 10.5 when incubated with L.A., and 50.1 +/- 9.7 in the Hanks controls. The statistical comparison between both series showed no significance. The mean active rosettes from the L.A. incubated cells was 33.7 +/- 9.4 and 33.8 +/-10.1 in the control group. Again the statistical significance was null as it was when each A.F. was compared with its control...