The immune response of human neonates to Listeria monocytogenes infection

Infection with Listeria monocytogenes during pregnancy has a high fetal and neonatal mortality. In rodents, it has been shown that resistance to Listeria infection is dependent upon a T cell-mediated immune response to the bacteria. The immune humoral and cell-mediated response to L. monocytogenes was studied in seven mother infant pairs who had documented evidence of L. monocytogenes sepsis. All studies were carried out 1 year following the initial infection as part of a clinical and immunological follow-up, and compared to an appropriate control group. The microagglutination titre and opsonizing activity of mothers previously infected with Listeria was significantly greater than that of the control mothers or their infected infants. There was no difference between the babies previously infected with L. monocytogenes when compared to control infants. The in vitro lymphoblastogenic response to Listeria, staphylococci, tetanus toxoid, and phytohemagglutinin was assessed. Infected mothers had a significantly greater proliferative response in the presence of Listeria than the control mothers, while the response of the previously infected infants was not different from that of the control infants. The response to the other antigens and PHA was similar in all groups. In conclusion, infants infected with L. monocytogenes during the perinatal period demonstrated neither a specific antibody response nor exhibited a cell-mediated immune response to these bacteria. These data support the idea that perinatally-infected infants have a markedly impaired immune response to L. monocytogenes and may, thus, explain their increased susceptibility to this infection.