References

The importance of the effect of genes of the major histo-compatibility system in relation to certain virus-induced lymphoid tumours in mice is well established (Lilly & Pincus, 1973). In studying the influence of this system on these murine tumours, congenic lines of mice were used which are effectively identical and homozygous at all loci except for the one under test. When seeking for an analogous situation in man, genetic diversity at many loci is a major confounding factor. Furthermore, in contrast to the known role of viruses in murine leukaemia, their role in human leukaemia and Hodgkin's disease has yet to be substantiated. It is therefore not surprising that the effects of the different phenotypes and genotypes of the HLA system in man on susceptibility and resistance to leukaemia and Hodgkin's disease have been suggestive rather than conclusive. Ginical heterogeneity may also militate against the detec-tion of real effects. The selection of patients and controls, including the means by which patients are ascertained, can cause difficulties in deciding whether particular factors in-fluence susceptibility or resistance. The effect of improved methods of treatment has also to be taken into consideration in assessing the role of the HLA system on survival. On the credit side much more is known about the manifestations of the leukaemias and related disorders in man than in any other species. Therefore there is scope for comparing the distribution of HLA antigens in patients with the same disease who show different pathological and prognostic features. In the diseases reviewed in this paper, family studies allowing haplotype deduction will become increasingly important, particularly in relation to the identification of factors that influence survival