Immune responses to administration of a vaccine against Haemophilus influenzae type B in splenectomized and non-splenectomized patients

Objectives: we investigated the cause of hypo-responsiveness to vaccines in splenectomized subjects, Methods: we evaluated the immune responses to a Haemophilus influenzae type b vaccine and the sizes of lymphocyte subpopulations in 25 splenectomized and 45 non-splenectomized thalassaemic patients, in 12 individuals who had been splenectomized after trauma and in 20 controls. Results: the immune response in the controls was significantly higher (P < 0.001) than in splenectomized patients after trauma and in both, the respon se was higher (P < 0.001) than in thalassaemic patients. In asplenic subjec ts after trauma, percentages of CD3 and CD4 cells were lower (P < 0.001) th an in patients in tile other groups: the controls had higher percentages of CDS cells (P < 0.001) than patients in the other groups, The natural logar ithm of the mean percentage of CD19 showed a quadratic trend from thalassae mic patients through asplenic subjects to controls (P < 0.001). Levels of C D16(+) natural killer (NK) cells were higher (P < 0.001) only in asplenic s ubjects after trauma, Conclusions: the significant decrease in the immune response of the splenec tomized thalassaemic patients vs. non-splenectomized thalassaemic patients may in part, be due to their basic immunological condition, Thus, the best strategy for protecting these subjects is to vaccinate them before the sple nectomy.