HLA-A TYPING TO ALLELE LEVEL IN DIFFEENT POPULATIONS.
          D. Middleton and F. Williams.   Histocompatibility and Immunogenetics Laboratory, City Hospital, Belfast, N. Ireland.
          High resolution PCR-SSOP typing methods for HLA-A identification have been established. The four systems, which operate independently of each other, are intended for use as secondary typing systems following HLA-A identification with a medium resolution PCR-SSOP techniique. The systems use DIG labelled probes for the identification of HLA-A alleles as follows:- (i) HLA-A*02 (25 probes); (ii) HLA-A*29 and -A*33 (6 probes); (iii) HLA-A*24 and -A*30 (24 probes) and (iv) HLA-A*11, -A*25, -A*26, -A*34 and -A*68 (21 probes). Applications of the methods to several population groups (N. Ireland, Singapore Chinese, Mexico, Brazil, Omani, Pima Indian) resulted in the detection of allelic variation within many of the serologically defined antigens. Within the N. Ireland population HLA-A*1101, -A*2402, -A*3402 and -A*6601 were detected as the only representatives of their respective allele group. Variations were detected within the remaining allele groups. While HLA-A*0201, -A*2501, -A*2601 and -A*2902 represented the majority of alleles within each allele group, HLA-A*0202, -A*0205, -A*2502, -A*2608 and -A*2901 were all detected in a small number of cases. HLA-A*3001 and -A*3002 were present in equal proportions, with -A*3004 detected in a few cases. HLA-A*3301 and -A*3303 were identified on a scale of 3:2 respectively. HLA-A*68012 was the most frequently identifed A68 allele with -A*68011 and -A*6802 occuring in equeal amounts. Of the other populations studied Singapore Chinese showed the greatest variation with respect to HLA-A*02 and -A*24 alleles with -A*0203, -A*0206, -A*0207, -A*0210, -A*2403, -A*2407 and -A*2410 being identified. HLA-A*0206 was detected in Pima Indian samples and -A*0208 in an Omani individual. All other alleles identified in the remaining population groups had been detected in the Northen Ireland population.