Comparative Measurement of Fetal Haemoglobin Levels And Their Association with Antibody Responses to Plasmodium Falciparum Antigens Among Sickle Cell Patients in Bondo Subcounty, Western Kenya

Abstract

ABSTRACT Plasmodium falciparum malaria infection remains one of the greatest global public health problems. However, studies have shown that fetal haemoglobin (HbF) protects against malaria in sickle cell disease (SCD) and HbF cooperates with antibodies to provide protection. Associations between HbF and antibodies have been done only on infants and therefore protection could be due to maternal immunity. Children at 5 years old have developed their own immunity and also HbF levels do not significantly change at this age. Bondo in western Kenya is one of the regions that have been affected by SCD recording a prevalence of 1.6% against a prevalence of 1.8 in western Kenya. Association of HbF levels and antibody responses to pre-erythrocytic and erythrocytic stage antigens of P. falciparum malaria has not been studied. Levels of HbF have been determined using Betke method but it produces falsely elevated values. High Performance Liquid Chromatography (HPLC) is more sensitive and precise but, its results have not been compared with that of Betke to determine the association of HbF levels with antibodies to malaria. Therefore this study sought to compare tests for HbF levels and relate them with the antibody responses to preerythrocytic and erythrocytic stage antigens of P. falciparum malaria infection among sickle cell patients above 5 years old in Bondo sub-county, Western Kenya. The specific objectives were; to correlate HbF levels using HPLC and Betke; to determine the association between HbF and antibodies to pre-erythrocytic stage antigens of P. falciparum malaria and to determine the association between HbF and antibodies to blood stage antigens of P. falciparum malaria. A cross sectional study design and purposive sampling was used to select 100 SCD patients. Using a sample size of 100, detectable effect sizes were obtained at 80% power and α of 0.05. HbF values were determined using HPLC and Betke methods and the quantification of IgG antibodies against P. falciparum recombinant antigens was done by the Multiplex Suspension Array Technology. Using pearson’s correlation test to compare HbF levels obtained by HPLC and Betke, the study reports that there was no statistically significant correlation between the two methods (r = -0.016) and therefore either method can be used to measure HbF levels. Linear regression showed that there was an association between HbF and antibodies to pre-erythrocytic antigens CSP (p = 0.040) and LSA (p = 0.002) when Betke method was used. However no associations were found when HPLC method was used. Fetal haemoglobin also showed associations with antibodies to erythrocytic antigens, GLURP-R2 when both Betke (p = 0.010) and HPLC (p = 0.049) methods were used and associations with erythrocytic antigens AMA-1-FVO (P = 0.001), AMA-1-3D7 (P = 0.002), MSP-3-FVO (p = 0.03), and EBP-2 (p = 0.044) when HPLC method was used. The study found other associations that could not be established based on Betke. The findings of this study have shown that HbF associates with antibodies to pre-erythocytic and erythrocytic antigens of P. falciparum malaria and therefore could influence protection against malaria infection. Association between HbF and antibody responses provides useful information that informs development of vaccine for malaria on individuals with SCD.