Induction of human cord blood lymphocyte proliferation by type III group B streptococci

In a preceding communication, the authors have described the selective adherence of group B streptococci (S. agalactiae) to human neonatal lymphocytes. In the present one, it has been shown that cord blood lymphocytes obtained from healthy newborns possess the ability to develop proliferative responses in the presence of type III group B streptococci. When investigating the influence of these bacteria on both adult and neonatal mononuclear cells (MNC), the following patterns of adherence and lymphocyte reactivity could be observed: (1) Type III group B streptococci adhered spontaneously to lymphocytes (11.4 +/- 5.7%, n = 14) of healthy newborns but not to those from adults, (2) The capacity to proliferate was restricted to cord blood lymphocytes giving a mean peak response at day five of culture in the presence of the bacteria (6.8 +/- 2.8 times over the background, n = 15), (3) The correlation between streptococcal adherence and cord blood lymphocyte proliferation was statistically significant for 10 independent experiments (r = 0.75, p = 5%), and (4) Type III group B streptococci inhibited the Pokeweed mitogen (PWM)-induced lymphocyte proliferation in adult but not in neonatal MNC cultures. The different pattern of reactivity between adult and cord blood MNC towards group B streptococci will be discussed.