HUMORAL AND CELLULAR IMMUNE RESPONSES TO PRP

Immune responses to Hemophilus influenzae, type b, polyribophosphate (PRP) were studied in 4 infants vaccinated at 6 months with 3 injections of PRP spaced 2 to 3 weeks apart. The injections totaled 1.6ugm of PRP mixed with 0.2ugm of cellular protein. Antibody to PRP was assayed by the Farr technique. Cellular responses were evaluated by incubating peripheral blood lymphocytes with several dilutions of pure PRP or PRP with protein and assaying for either protein or DNA synthesis. Generally significant increases in antibody to PRP were not seen as a result of this vaccination. No pre or post-vaccination lymphocyte cultures displayed increased DNA synthesis to the various dilutions and preparations of PRP tested. On the other hand, post-vaccination lymphocyte cultures from 2 infants displayed increased protein synthesis to pure PRP and one of these infants reacted similarly to PRP-protein. A third infant had significant pre-vaccination stimulation of protein synthesis and remained so following vaccination. The significance of cellular immune responses to PRP is unknown, however since antibody to PRP is not normally generated in the young infant, evaluation of both humoral and cellular immune responses may reveal additional mechanisms of immunity to infection with H. influenzae.