Lymphocytes co-ordinate the immune system’s response and play a central role in cell mediated immunity . Lymphocyte subset may include; Helper T cells (CD4 T-cells), Cytotoxic T cells (CTLs or CD8 T-cells), Memory T cells and Regulatory T cells (Treg cells). Upon encounter with antigens, CD4 T cells become activated and proliferate rapidly secreting cytokines that sends signals and maintain active immune response. On the other hand, the CD8 T-cells destroy virally infected cells and tumor cells, and remain inactivated when there is no foreign antigen. In human immunodeficiency virus-1 (HIV-1) infected individuals, lymphocytes (specifically CD4 T-cells) are the viral prime targets. Therefore in these individuals, a CD4 count provides a picture of immune system competence, with higher CD4 counts typically signifying healthier immune systems [1, 2]. In such application, flow cytometry is used to provide absolute counts, percentages and or ratios of these lymphocyte subsets. Besides HIV management, flow cytometric analysis of peripheral blood lymphocyte phenotypes has proven a useful aid in managing a wide range of medical conditions, including autoimmunity, immunodeficiency, infection, malignancy and transplantation [3–5]. Essential to the effective application of this approach is availability of accurate reference values against which results can be meaningfully compared.
Reference ranges that are currently used in Kenya are derived from data obtained from Caucasians who are not African Kenyans. In addition, these ranges do not include age and sex which are very important factors that influence lymphocyte counts . Furthermore, several factors have been associated with these differences in lymphocyte counts. These may include; demographic and genetic factors, current exposure to infectious diseases and behavioral factors on CD3, CD4 and CD8 in HIV-negative populations [1, 2, 6]. Averagely, healthy African and Asian populations have been shown to have lower CD4 lymphocyte counts than their western European and Caucasian counterparts [2, 7, 8]. In addition, women tend to have higher CD4 levels than men with comparable demographic and behavioral patterns [8, 9]. However, there is still limited data from specific countries to confirm these differences.
The pattern of lymphocyte generation has been shown to affect the levels of circulating lymphocytes in males, females and individuals of different ages. The pattern of T lymphocyte generation in aging has been associated with dynamic changes in thymic and extrathymic functions along with sequential developmental steps from cells to mature cells . Increased absolute numbers of peripheral blood CD4 cells in females compared to males have been reported . This is perhaps due to androgens which accelerate thymocytes apoptosis and subsequently influence T cell repertoire with males tending to have less CD4 cells than females [12, 13]. Sex and age related variations in the lymphocyte subsets contribute to age and sex related diseases including autoimmune disorders in females and leukemia or lymphoma in males and elderly patients [14, 15]. Other factors which have received little attention but also affect the normal lymphocyte levels include; dietary patterns, body mass index and smoking habits [16–18]. The influence of these many factors point out to the fact that the reference ranges of one population might not be accurately used as a reference range for another. This might give an inaccurate interpretation of the immune status of the individuals.
Several efforts to establish reference ranges have indicated differences in lymphocyte levels between African and Western populations [2, 3, 9, 19]. In one community in Kenya, general clinical ranges have been shown to significantly differ from the ranges from other parts of the continent . These ranges are also appreciably different from those reported in a neighboring country . The two studies in Kenya had indicated a possibility of having remarkably different ranges of lymphocyte subsets within the Kenyan population [20, 22]. This necessitates the need for a comprehensive reference range establishment using subjects from different regions of the country. In this study we report comprehensive reference ranges for CD3, CD4 and CD8 cutting across representative regions of the country. The study provides ranges specific for males, females and for different ages.