FETAL PERIPHERAL-BLOOD MONONUCLEAR CELL PROLIFERATIVE RESPONSES TO MITOGENIC AND ALLERGENIC STIMULI DURING GESTATION

Blood samples were obtained from fetuses and premature babies (n=51) ( 15-34 weeks gestation) to determine at what stage the fetal immune sys tem was able to produce a positive proliferative response to common al lergens. Peripheral blood mononuclear cells (PBMC) were stimulated wit h the mitogen, phytohaemagglutinin (PHA), and the allergens, house dus t mite, cat fur, birch tree pollen, beta-lactoglobulin, ovalbumin and bee venom (mellitin). Results were expressed as ratios of stimulated t o unstimulated H-3 thymidine incorporation, and as percent positive re sponders. There was an increase in proliferation ratio which correlate d with increasing gestational age for PHA (p<0.0001), cat fur (p=0.042 ), birch pollen (p=0.022) and beta-lactoglobulin (p=0.006). The point in gestation when cells from some individuals began responding to the allergens with a ratio of 2.0 was at approximately 22 weeks. PBMC prol iferative response ratios were higher from samples from babies > 22 we eks gestation compared to < 22 weeks for the mitogen and all allergens , except mellitin. There was also a greater proportion of positive res ponders from samples > 22 weeks compared to < 22 weeks for the mitogen and all allergens, except mellitin. Maternal exposure to birch pollen , which has a discrete season, was assessed to determine whether expos ure had occurred at 22 weeks gestation or beyond. Results showed a hig her proliferative response in infant cells stimulated with birch polle n (p=0.005) and higher proportion of positive responders (p=0.01) in t he group of babies whose mothers had been exposed to birch pollen beyo nd 22 weeks, compared to those whose mothers had not been so exposed. These results suggest that in utero fetal exposure to an allergen from around 22 weeks gestation may result in primary sensitisation to that allergen, leading to positive proliferative responses, at birth.