Abdul Hannan ( Armed Forces Institute of Pathology, Rawalpindi. )
Masood Anwar ( Armed Forces Institute of Pathology, Rawalpindi. )
Tahir Aziz Ahmed ( Armed Forces Institute of Pathology,Rawalpindi )
Lubna Zafar ( Armed Forces Institute of Pathology,Rawalpindi. )
Farhat Rizvi ( Armed Forces Institute of Pathology,Rawalpindi. )
Manzoor Ahmad ( Armed Forces Institute of Pathology, Rawalpindi. )
HLA frequencies on 1231 subjects from within the country, using methods employed by National Institute of Health, USA is reported. Pakistani population appears to be a mixture of an indigenous population with others particularly Orientals and Negroids. Relationship with Caucasians is not convincing (JPMA 40 : 294, 1990).
The HLA system is known to be the most polymorphic genetic system found in humans. It plays a vital role in transplantation, immune responses, disease associations, paternity testing and anthropological studies. Accordingly, a number of studies have been carried out on different populations and ethnic groups to collect basic data on their antigen and gene frequencies. Studies have been carried out on HLA frequencies in Pakistanis settled in other countries1-3. Not only the number of subjects tested in such studies are limited, the purity of their ethnic origin is also suspect. A study of HLA system has, so far, not been reported from within Pakistan. This study presents the HLA frequencies in Pakistani population.
MATERIAL AND METHODS
A total of 1231 subjects (920 males and 311 females) were tested for HLA-A and B loci. Only 220 subjects (159 males and 61 females) were tested for HLA-C locus. The class II antigens (HLA-DR and HLA-DQ) were tested in 1166 subjects (862 males and 304 females). The age of subjects ranged from 3 years to 65 years. All the subjects were either prospective recipients of renal/bone marrow transplant or prospective donors. Donors included both related and non-related donors. Details are shown in Table-I.
Venous blood samples were collected in heparinized vacuutainer tubes and were processed within 12 hours. The lymphocytes were separated on Ficoll-Hypaque density gradient by centrifugation in a refrigerated centrifuge. The B cells were separated by adhesion to nylon wool in a column4. The HLA antigens were tested by the two stage NIH microlymphocytotoxicity assay using Terasaki plates4. Antisera were obtained commercially from Biotest, Pel-Freeze and Behring Laboratories. The relative antigen frequencies were determined and gene frequencies were estimated from antigen frequencies using the formula p = 1-/1-f where p denotes the gene frequency and f denotes the antigen frequency4. AB haplotypes were then calculated from these frequencies.
The existence of histocompatibility antigens was first proposed by Landoteiner in 1931 in his Nobel lecture6. Gorer, in his pioneering work on mice, proved the existence of such a system6. The work carried out by Dausset, van Rood and Payne led to the formation of a base for a comparable system in man, and the system was named “the human leucocyte antigen (HLA) system” 6.Its development to present stage would not have been possible without international collaborative efforts. A system of workshops was initiated by D.B. Amos in 1964 (which still continues). It added new dimensions to this very important and most polymorphic antigen system6. The fourth and fifth International Histocompatibility Workshops, organized in 1970 and 1972, assembled data from over 100 different populations and found that the frequencies of HLA antigens varied markedly from one ethnic group to another7. Such observations have helped to gain an insight into the origins and associations of various populations. Earlier studies in HLA system in Pakistanis have tried to place this population at its place in anthropological map of the world2,3. There has been a general opinion that Pakistani population is more near Caucasians. But if we compare first 5 most common antigens of each locus in different population groups, a different picture emerges.
Table VIII shows antigen and gene frequencies for these after excluding antigens which are shared by all population groups as first five most common antigens. Detailed comparison of all antigens is shown in tables II to VI. Our findings suggest that Pakistanis are closer to Orientals and Negroids, rather than Caucasians. Only one class I Antigen (Ai) is shared by Pakistanis and Caucasians as one of first five most common antigen groups (1/5) while 4/5 and 3/5 class I antigens are shared with Orientals and Negroids, respectively. One antigen B17 appears to be most prevalent in Pakistanis only. Among class II antigens 2/5 are shared with Caucasians and Negroids while 1/5 is shared with Orientals. One antigen (DRi) appears to be most prevalent again only in Pakistanis. These figures suggest mixing of an indigenous population mostly with Negroids and orientals but also with Caucasians. A detailed study of HLA system in various castes and tribes may produce very interesting results. In table-VII at many points the true frequency of AB haplotype is much higher than expected. This is called linkage disequilibrium. This is particularly evident for A28 B5, Aio, B8 and A1, B17. Most likely this is because of presence of greater number of related persons in our study. Proportion of blanks (x) is also higher as compared to other studies. This may be due to absence of about 18 antisera from our plates. This is only the beginning of studying HLA system in Pakistan. More studies are required to establish concrete basis of this system for our population.
1. Singal, D.P. The distribution on HLA Leucocyte Antigens in In. dians, in Histocompatibility testing. Copenhagen, Munksgaard, 1972; p.179.
2. Harris, R., Wentzel, J., Carroll, C.A. and Jennison, R.F. HLA frequencies in West Pakistanis (Punjabi) in the United Kingdom, in histocompatibility testing. Copenhagen, Munksgaard, 1972, p.163.
3. Solheim, B.G., Bratlie, A. and Thorsby, E. A study of the HLA system in a West Pakistan population, in histocompatibility testing. Copenhagen, Munksgaard, 1972, p.171.
4. Staff of NIH, Transplantation and Immunology Branch. NIAID manual of tissue typing techniques 1979-1980. U.S. Deptt. of Health and Human Services, NIH Publication No. 85-545; 1980, p.39.
5. Albert, E.D., Baur, M.P. and Mayr, W.R. Population analyses on the basis of deduced haplotypes from random families, in histocom patibility testing. New York., Springer — Verlag, 1984.
6. Bodmer,W.RTheHLAsystem: Introduction. Br. Med. Bull., 1978;34:213.
7. Ting, A. and Morris, P. J. The relationship of six ethnic groups (Chinese, Malays, Indians, New Guinea highlands and coastal natives, Australian, Caucasians). Based on the HL-A System, in histocompatibility testing. Copenhagen, Munksgaard, 1972, p.275.