Increased memory phenotypes of CD4+ and CD8+ T cells in children with sickle cell anaemia in Tanzania.

Background: Infection is an important cause of morbidity in children with sickle cell anaemia (SCA). However, little is currently known regarding the spectrum of adaptive immune derangement in SCA, especially of populations in Sub-Saharan Africa. In this study, we investigated the phenotype and activation status of T and B lymphocytes among children with SCA in Tanzania.

Methods: We compared 30 children with SCA aged 1-6 years in steady-state with 10 age-matched controls. We assessed white blood cell count, T and B lymphocyte phenotype and activation status using an automated haematology analyser and multiparameter Flow Cytometry.

Results: In children with SCA, the absolute lymphocyte, monocyte and granulocyte counts were all increased. There was also an increase in proportion of central/transitional memory (42.4% vs. 33.3%, p = 0.0100), effector memory (7.8% vs. 5.4%, p = 0.0086) and terminally differentiated (2.3% vs. 1.3%, p = 0.0355) CD4+ T cells as well as effector memory CD8+ T cells (21.3% vs. 11.5%, p = 0.0060) in children with SCA. In contrast, there was no difference in naïve, classical memory, atypical memory and IgM memory B-cells between the two groups. The level of activation of both T and B cells were comparable between children with and without SCA. Furthermore, we observed a significant inverse correlation between frequency of the effector memory CD8+ T cells and haematocrit (Spearman rho = -0.3859, p = 0.0352).

Conclusions: Children with SCA in Tanzania show an absolute increase in all leukocyte types, including lymphocytes, with skewing of both CD4+ and CD8+ T cells towards the memory phenotypes. These findings provide insights on the development of adaptive immunity which may have implications on vaccine responsiveness, allo-immunisation, auto-immune diseases and transplant immunology in children with SCA.