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 response was higher (P < 0.001) than in thalassaemic patients. In asplenic subjects after trauma, percentages of CD3 and CD4 cells were lower (P < 0.001) than in patients in the other groups; the controls had higher percentages of CD8 cells (P < 0.001) than patients in the other groups. The natural logarithm of the mean percentage of (CD19 showed a quadratic trend from thalassaemic patients through asplenic subjects to controls (P < 0.001). Levels of CD16+ natural killer (NK) cells were higher (P < 0.001) only in asplenic subjects after trauma. CONCLUSIONS: the significant decrease in the immune response of the splenectomized 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 splenectomy.

Low serum levels of interleukin-6 in children with post-infective acute thrombocytopenic purpura.

Interleukin-6 plays an important role in host defense mechanisms and it appears to be a major mediator of the acute-phase response. IL-6 is also an important thrombocytopoietic factor. High serum levels of IL-6 are present in reactive thrombocytosis. The number and function of circulating platelets are the major factors that affect megakaryocytopoiesis by thrombopoietin. High levels of thrombopoietin have been observed in patients with thrombocytopenic purpura. To evaluate a possible thrombopoietin-like function of IL-6, we measured IL-6 levels in the serum of patients affected by post-infective acute thrombocytopenic purpura using a sensitive ELISSA assay. As controls, we studied normal subjects and patients with reactive thrombocytosis. No significant difference was observed between thrombocytopenic patients and normal controls. High IL-6 levels were present in patients with reactive thrombocytosis. In conclusion, we had not observed high levels of IL-6 in acute thrombocytopenic purpura and, very probably, IL-6 is not involved in the regulation of platelet mass for the hemostatic function. The thrombocytopoietic activity of IL-6 is another acute-phase response and it is consistent with the other functions of this cytokine. This suggests an active participation of platelets in host defense mechanisms.