Identification of potential risks of platelet alloimmunization in sub-saharan African populations

Specific antiplatelet alloimmunization directed against Human Platelet Antigens (HPA) as neonatal alloimmune thrombocytopenia (NAIT), platelet transfusion refractoriness (PTR) or post-transfusion purpura (PTP) is far from uncommon. This study aims at identifying such a risk in the context of the diversity caused by the population migrations now observable in our hospitals today and particularly in the Sub-Saharan African (SSA) populations. 154 Beninese, 118 Cameroonians and 125 Congolese (Kinshasa) blood donors were genotyped for HPA by PCR-RFLP and -SSP. The most important risk for anti-platelet alloimmunization could be associated with HPA-2, as we observed a relatively high frequency of HPA-2b homozygous individuals (4% in Congo to 7,6% in Cameroon). As opposed to Caucasian populations, the risk of anti HPA-1a alloimmunization is extremely slight, due to the low frequencies of HPA-1 b homozygous individuals in SSA (0.8% to 1.3%). We observed an increase in the frequency of HPA-5b homozygous individuals (Cameroon 7.6%, Congo 5.6%, except for Benin 0.6%). The distribution of HPA-15 alleles is heterogeneous and HPA-3 alleles have similar distribution (HPA-3bb 11% to 16.8%) than Caucasian populations. In conclusion, HPA-2 alloimmunization should be looked for when NAIT, PTR or PTP is suspected, and to a lesser degree HPA-5 in the Congolese and Cameroonians. We have shown in Caucasians a strong association of anti HPA-5b immunization with a cluster of HLA-DR molecules sharing Glu-Asp at position 69-70 of the DR beta 1 chain. As this cluster is conspicuously present in these populations, it would be of interest to determine if this genetic background plays a role in immunization in those populations.