Vol. 36
1994
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Issue 1/2 Vol. 36 1994 |
The major histocompatibility complex (MHC) is a gene cluster that constitutes the main factor in determining immunological individuality. Due to their functional difference and their distinct patterns of expression the genes of the MHC fall into two classes: MHC class I and MHC class II. Both are involved in antigen recognition, while the genes in class I play an additional role in tolerance induction. Tolerance induction is a primary necessity in vertebrates which have evolved an anticipatory immune system. Therefore, analogous genetic systems have been identified in all vertebrates studied so far. For the moment two species should be considered: The MHC of the mouse is designated as H-2 (located on chromosome 17) and that of humans as HLA (human leucocyte antigens, located on chromosome 6).
The most prominent feature of the MHC in natural populations of most species is its extraordinary genetic diversity. Four characteristics of this system are responsible for its enormous diversity: 1) A number of functional loci per class. 2) allelopolymorphism (e.g. estimations for HLA class I ranging up to 60 different alleles per locus). 3) Codominant expression. 4) A high level of heterozygocity (in natural populations of mice it is almost 100%).
This high level of heterozygocity seems to be maintained by behavioural factors which are actively engaged in controlling reproductive success (Potts & Wakeland, 1990). In order to influence behaviour the MHC has to be expressed as an external signal. As studies in mice, rats and humans have revealed the MHC is associated with the expression of olfactory cues (Yamazaki et al., 1991; Roser et al., 1991; Ferstl et al., 1992). In mice these signals contribute to the phenomenon of imprinted mating preferences which serve to promote heterozygocity. Results which confirm this hypothesis stem from studies of inbred strains as well as semi-natural populations (Boyse et al., 1991; Potts et al., 1991). A possible second influence of the MHC on reproduction could also be shown in combination with the well-known pregnancy block effect (Bruce-Effect) (Yamazaki et al., 1983). Both of these influences rely on chemosensory imprinting and therefore are dependent on the level of general genetic diversity in a population (Beauchamp et al., 1988). By means of these mechanisms small populations with a high degree of inbreeding seem to be capable of maintaining the necessary level of genetic diversity in the MHC (Boyse et al., 1990).
First hints of similar effects on the social behaviour in humans came from two types of studies: 1) A series of population studies on the occurrence of shared HLA types in couples in part confirm an influence of the MHC but are not conclusive (Rosenberg et al., 1983; Giphart & D'Amaro, 1983; Nordlander et al., 1983; Pollack et al., 1982). 2) The target of our own studies was to demonstrate an HLA-associated odour expression in man and its effects on social perception.
In a field study 400 women were interviewed about the noticeable body odours of other people. 19 women reported strong sensations due to the body odours of a number of other persons. Effects of hygiene, certain perfumes and nutrition were controlled. Additionally, these women were asked to index control persons with neutral body odours. HLA typing of the women and all the indexed persons was provided. A comparison between the absolute numbers of negative, neutral and positive valence of indexed females and males reveals an equal distribution in females and an obvious trend in males. Most of the body odours of males were rated negatively.
A comparison of genetical similarity in indexed females and males by counting the shared alleles of indexing females with indexed persons reveals two effects: 1. The indexing women have a higher communality in their alleles with indexed females than with males. 2. Males for whom negative body odours were reported show a higher genetic similarity than those for whom positive body odours were reported.
The genetic similarity observed is in part due to the occurrence of a high frequency of certain HLA types (HLA A9/B15) compared with the base rate expected from a ten thousand sample. Indexing women, persons with negative and positive body odours differ significantly from the expected frequency. Controls (neutral) did not differ from the base rate.
The analysis of the serum concentration of sHLA reveals that persons with an HLA type A9/B15 show a threefold concentration than persons with other specificities. This is in accordance with a model extended by our group which postulates a central role of soluble HLA molecules in the expression of olfactory cues associated with the MHC.
Further studies using psychophysical methods should test whether the similartiy of body odours is indicative of genetic relatedness. Determining the relative importance of MHC associated body odours in social perception and in the regulation of social behaviour deserves further research.
Keywords: major histocompatibility complex, MHC, immune system, immunogenetical variability, body odour, olfactory
Short Title: Eggert, F. et al. (1994) PsyBeit 1-2:152
Dr. Frank Eggert[Pabst Science Publishers] [Psychologische Beiträge] [Table of Contents] [Search] [Order]
