Secretor status, fucosyltransferase 2 (fut2) gene polymorphisms and susceptibility to HIV infections among female sex workers in Nairobi, Kenya

Abstract

Blood group antigens are expressed on red blood cells however; these antigens can also be expressed on some other cells particularly on the surface of epithelial cells and may be found in mucosal secretions. The gene known to determine the secretion of these blood group antigens is the Secretor Fucosyltransferase 2 (FUT2) gene. In many human populations 80% secrete ABO antigens (termed secretors) while 20% do not (termed nonsecretors). Furthermore, there are disease conditions that are associated with secretor status. It is against this background that this study was proposed. Hypothesis: There are correlations between Secretor FUT2 gene polymorphisms and blood group antigen secretor status; non-secretors are less susceptible to HIV infections. Broad Objective: To investigate associations between mucosal blood group antigen expression profiles (secretor status), Secretor FUT2 gene polymorphisms and susceptibility to HIV infection among female sex workers in Nairobi, Kenya. Study Design: This was a cross-sectional study. Study Area: This study was conducted at the Nairobi Regional Blood Transfusion Centre, and at sex worker outreach program clinics, from the Pumwani Majengo female sex worker cohort, Nairobi, Kenya. Study Population: This study enlisted 142 adults of both gender (male and female, aged 18-65 years) from the regional blood transfusion centre in Nairobi, Kenya. In addition, this study recruited 280 female sex workers from the well-established Pumwani Majengo cohort aged 18 to 65 years of age (n=422). Materials and Methods: Blood, saliva and female genital tract (vaginal and cervical) specimens were collected from each study participant once informed written consent was obtained. The laboratory analyses were carried out at the KAVI Institute of Clinical Research (KAVI-ICR) and the University of Nairobi Institute of Tropical and Infectious Diseases (UNITID) laboratories, Nairobi. Blood typing was determined using standard serological techniques using monoclonal antibodies to the ABH, Rhesus (D) and Duffy (Fya, Fyb) blood group antigens. Secretor phenotyping was determined using lectins specific to blood group H antigen in both salivary and female genital tract samples. This was correlated to the HIV sero-status. The correlation of secretor phenotypes to CD4+ T cell counts, was based on retrospective data analyses, following immunophenotyping using a CD3/CD4/CD45 panel on an BD LSR II flow cytometer. For secretor genotyping, DNA was extracted from frozen whole blood samples. Quantitative real-time amplification was performed based on the polymerase chain reaction (PCR) on a Rotor-gene Q (Qiagen) and PCR products sequenced on the next-generation pyrosequencer, Pyromark Q24 platform (Qiagen). Results: Objective 1: ABO blood group phenotype frequency distribution was O>A>B>AB comprising 199 (47.2%), 120 (28.4%), 84 (19.9%) and 19 (4.5%) respectively with 408 (96.7%) Rhesus (D) positive cases. Duffy positive phenotypes were reported in 2 (0.47%) of the study participants. Objective 2: Saliva testing showed that among the blood donors, 121 (85%) were secretors and 21 (15%) were non-secretors, while among the female sex workers, 212 (76%) were secretors and 68 (24%) non-secretors Objective 3: Based on HIV screening, 92 (32.9%) of the female sex workers were HIV-1 infected and 188 (67.1%) HIV-1 uninfected. There was a correlation between HIV infections and secretor phenotypes. The proportion of secretors was significantly higher among women with HIV infection (77/92 = 83.7%) in comparison to HIV un-infected women (135/188 = 71.8%) (p=0.029). Furthermore, the incidence of HIV infection was significantly higher among blood group A secretors (p=0.028) in comparison to O secretors, but not B and AB. Objective 4: The correlation to CD4+ T cell counts demonstrated, although the secretors were more susceptible to HIV, following infection, the ABH secretors maintained elevated levels of CD4+ T cell counts in comparison to non-secretors and this difference was statistically significant (p=0.005). Objective 5: Secretor FUT2 genotyping demonstrated the secretor status of the population was not dependent on the allele at position 428 as has been previously reported in African populations, suggesting the secretor and non-secretor phenotype profiles may be due to novel polymorphisms in the Kenyan population. Conclusion: The prevalence of ABO, Rhesus and secretor/non-secretor phenotypes are similar to the global profiles as previously reported across African populations. However, the underlying genotypic variation resulting in the non-secretor phenotype in a subset of the Kenyan population as screened among our study cases does not fall under a the „se428 umbrella‟ of a restricted geographical distribution as has been previously reported. These findings further suggest the non-secretor phenotype may confer a certain degree of protection against HIV infection, as there were higher HIV infection incidence rates among ABH secretors; but following infection, the same population of secretors maintained elevated CD4+ T cell counts. Recommendations: 1. It is important to know the frequencies of various blood group antigen phenotypes in a population. This information is important to confirm the prevalence of both major and minor blood group phenotypes in a population. There are a number of blood group phenotypes, which have been associated to varying disease/infection susceptibilities as seen in this study, blood group A individuals were at an increased risk for HIV infections. 2. Secretor and non-secretor phenotype profiles in populations should be determined. This data serves as a baseline for investigative studies on the correlation between secretor and non-secretor phenotypes and associations to disease conditions. In the Kenyan population, secretors were found to have a significantly higher incidence of HIV infection rates. 3. HIV awareness programmes, should include information on secretor status testing as individuals who are ABH secretors are at an increased risk of HIV infections. 4. HIV treatment and care packages, should include secretor testing as non-secretor individuals have been shown to progress faster to infection, based on a rapid decline in CD4+ T cell counts in comparison to the secretor counterparts. 5. Secretor testing should be comprehensive, based on both phenotyping and genotyping. There may be silent and/or novel mutations specific to a population, which confer varying phenotypic traits, hence dual screening will ensure an individual is ascertained of their secretor status.