Allotypes exclusion

Allelic exclusion of allotypes is more complex than the exclusion of X linked traits in that several unlinked loci are involved. Nonetheless, a strong analogy may be drawn between the two phenomena. As in the exclusion of X alleles, allotype exclusion may be random and it is permanent in that peripheral blood lymphocytes and their progeny continue to produce the same allot)rpes . Whether the entire chromosome is involved is not known, nor is it known whether activation or inactivation is the basis of allelic selection of allotypes. 

Allotypic exclusion of Ig was indirectly demonstrated when patients with polymyeloma were inspected (Harboe et al., 1962 Martensson, 1963 Martensson and Kunkel, 1965 Cohn, 1967). It was demonstrated that in heterozygotes the heavy chains of myelomic proteins have only one allotype, whereas in the blood of the same individuals both allotypes are present (Table 21). 

Kelus and Gell (105) and Sell (106) first described allotypic determinants present on rabbit IgM but not on IgG or IgA. Their exclusive presence on IgM molecules is presumptive evidence that the determinants are on p. chains rather than on L chains. Five markers have been described Msl, Ms2, Ms4, Ms5, and Ms6 (107,108) another... 

Recently published papers have demonstrated the allelic exclusion which occurs in the Lpp locus of pigs (Rapacz and Master, 1968), the Ac locus of Ig (Vice et al., 1970), and the Lpg locus of lipoprotein allotypes (Albers and Dray, 1969). Analysis of the Ess locus of a-arylesterase (Albers et al., 1969) and A locus yA Ig (Conway et al., 1969) in rabbits allowed the suggestion that functional haploidy of autosomal genes could occur comparatively often. 

Lymphoid tissue of animals heterozygous for either Ig locus is represented apparently by two competitively developed cell populations as a result of allelic exclusion. These populations are possibly under selection caused by certain factors. Thus, variations in the proportion of cells with different allotypes could occur. This selection is the best natural explanation of variation in the quantitative ratios of serum Ig s with the different allotypic constitutions in heterozygous individuals (Oudin, 1966). 

The mechanism which determines the phenotypic restriction of allotypes appears to act only in vivo since there is an absence of allelic exclusion in in vitro clones of lymphoid cells (Bloom et al., 1971). 

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