im*mmology bntay, Seplember 1981
170
T L molecules of the T l a region e'3. The class I M H C products are present on nearly every cell in the organism whereas their T l a counterparts occur in more lim~UdJdistribution and have been described mainly on lymphoid cells 4. The structural and functional relationships among the K, D and L glycoproteins have been the subject of an intense study which includes detailed primary structural analysesL O n the contrary, little is known about the Qa and T L products. A major breakthrough in this area has recently been reported by Soloski el al. 6, who have isolated Qa-2 molecules and compared their structures to those of K and D molecules from the same haplotypes. Because Qa-2 molecules are expressed on resting spleen cells at levels too low for structural analysis, the Qa-2 molecules used in this study were isolated from mitogen-stimulated spleen cells. Use of the sequential immunoprecipitation technique indicated that the Q a determinants were on molecules separate from those carrying the K and D antigens. A comparative peptide mapping technique was then used to determine the degree of similarity among the Qa-2, H-2K and H-2D molecules. In this technique one molecule is intrinsically radiolabeled with [3H]arginine and the other molecule with [14CJarginine; the immunoprecipitated molecules are combined and digested with the proteolytic enzyme trypsin; and the resultant peptides are analysed by ion exchange chromatography. These analyses indicated that the Qa-2 molecule has between 21 and 43% of its tryptic peptides in c o m m o n with the K and D molecules. By analogy to K and D products for which both primary structure and peptide mapping data are available, it can be estimated that the Qa-2 peptide comparisons indicate an amino acid sequence homology of 75-90%; that is to say, Qa-2 is as similar to an H-2K molecule as H-2K is to H-2D. Extrapolation of these data leads to the suggestion that there are a p p r o x i m a t e l y 10 h i g h l y h o m o l o g o u s class I glycoprotein molecules synthesized by genes in the M H C and T l a regions. Soloski and co-authors argue that this similarity indicates that these loci arose from replicates of a primordial gene which susequently diverged to the present closely related forms. It is further argued that the presence of cell-surface structures resembling Q a and T L in the guinea pig and h u m a n suggests that the gene duplication events
occurred prior to speciation. While it is difficult to argue with the postulate of gene duplication, the precise timing of such a duplication may require further data. The murine M H C class I molecules have a number of species-specific residues in common, that is, residues which are present on all murine molecules but on no human class I M H C molecule. The existence of these residues would argue that certain of the duplication events occurred after divergence of the evolutionary pathways that led to the mouse and human. The effect of the common biochemical properties of the various class I molecules on the primary structure must also be considered before constructing detailed hypotheses. Each is a membrane glycoprotein and each binds 132-microglobulin in a non-covalent fashion. There are no extensive structural requirements for the addition of carbohydrate units and a number of different amino acid sequences appear equally to serve the function of membrane binding. The nature of the structure required to non-covalently bind ~2-microglobulin is at present obscure although there appears in each of the class I moleculesa domain (residues 181-270)with a highly conserved structure that bears some homology to the immunoglobulin constant region domain. It may be questioned whether a rigorous requirement for identity in this region with little homology in other domains would completely account for the results obtained in the peptide mapping studies. Thus, the high degree of similarity among the M H C and T l a class I antigens remains to be more completely defined and related to their respective functions. T. j. KINDT
Laboratory of hnmunogenetic.~, Natiorml lnslilule of Allergy and Infectious Diseases, Bethe~da, MD 2020,5, U.S.A.
References l Klein, J. (1975) in Biology of lke 3 louse /lislocompatibilil}, Complex New York, Springer-Verlag 2 Flaherty, L. (1980) in The Role of the Major Histocornpatibility Complex in Immunobiology (Doff, M.ed., in press) 3 Michaelson, J., Flaherty, L., Vitetta, E. and Poulik, M. (1977) J. Exp. Med. 245,1066 4 Stanton, T. H., Calkins, C. E., Jandinski, J., Schendel, J., Stutman, O., Cantor, H. and Boyse, E. A. (1978) J. Exp. Med. 148,963 5 Coligan, J. E., Kindt, T. J., Uehara, H., Martinko, J. and Nathenson, S. G. (1981) Nature (London) 291, 35-39 6 Soloski, M.J., Uhr, J. w., Flaherty, L. and Vitetta, E. S. (1981) J. Exp. Med. 153, 1080-1093
IgG heavy chain (Gin) allotypes in diabetes Considerable interest has been focussed on the genetic polymorphisms which control the immunoglobulin (Ig) allotypic determinants of the heavy chain and their possible associations with certain diseases which are believed to have an autoimmune basis. Although Elsevier/North-Holland Biomedical Press 1981 0167 - 4919/81/0000 - 0000/$02.50
there seems little doubt that the major genetic susceptibility to diseases such as Type 1 (insulindependent) diabetes, autoimmune thyroid disease, and Addison's disease is determined by genes in the H L A complex there are several facets of tile immuno-
immlmology loday, 5'eplember 19~W
genetic basis to these p r o b l e m s w h i c h r e m a i n unresolved. For example, the distribution of organspecific autoantibodies - ' c l a s s i c a l ' islet-ceil antibody, thyroid microsomal antibody and gastric parietal cell a n t i b o d y - in the nonaffected siblings of T y p e 1 diabetic p r o b a n d s is independent of the potential H L A genetic susceptibility, as j u d g e d by the H L A haplotype concordance with the p r o b a n d ~. In other words, if there is a genetic control of a u t o a n t i b o d y production, it is clearly separate from the genetic predisposition to pancreatic B-cell injury. I m m u n o g l o b u l i n allotypes have been investigated in a variety of populations indicating that certain G m haplotypes are particularly prevalent in Mongoloids and other ethnic groups 2. F r o m the evidence currently available, the G m locus is not on the short a r m of chromosome 6, although its exact location remains unknown. Most of the studies on G m allotypes and disease have been done in .Japan. Large numbers of serum samples from patients with various a u t o i m m u n e diseases have been investigated using a haemagglutination inhibition test on microflocculation slides employing officially recognized G m antiseraL~ The nine phenotypes observed in the J a p a n e s e p o p u l a t i o n could be assigned to four groups (Gml'21; Gml,2,2'; G m 1,13,15,1(' and GmI,:L~,I3). The G m 1,2,21 group was found in 36% of patients with myasthenia gravis compared with 16% of healthy controls (p
170
T L molecules of the T l a region e'3. The class I M H C products are present on nearly every cell in the organism whereas their T l a counterparts occur in more lim~UdJdistribution and have been described mainly on lymphoid cells 4. The structural and functional relationships among the K, D and L glycoproteins have been the subject of an intense study which includes detailed primary structural analysesL O n the contrary, little is known about the Qa and T L products. A major breakthrough in this area has recently been reported by Soloski el al. 6, who have isolated Qa-2 molecules and compared their structures to those of K and D molecules from the same haplotypes. Because Qa-2 molecules are expressed on resting spleen cells at levels too low for structural analysis, the Qa-2 molecules used in this study were isolated from mitogen-stimulated spleen cells. Use of the sequential immunoprecipitation technique indicated that the Q a determinants were on molecules separate from those carrying the K and D antigens. A comparative peptide mapping technique was then used to determine the degree of similarity among the Qa-2, H-2K and H-2D molecules. In this technique one molecule is intrinsically radiolabeled with [3H]arginine and the other molecule with [14CJarginine; the immunoprecipitated molecules are combined and digested with the proteolytic enzyme trypsin; and the resultant peptides are analysed by ion exchange chromatography. These analyses indicated that the Qa-2 molecule has between 21 and 43% of its tryptic peptides in c o m m o n with the K and D molecules. By analogy to K and D products for which both primary structure and peptide mapping data are available, it can be estimated that the Qa-2 peptide comparisons indicate an amino acid sequence homology of 75-90%; that is to say, Qa-2 is as similar to an H-2K molecule as H-2K is to H-2D. Extrapolation of these data leads to the suggestion that there are a p p r o x i m a t e l y 10 h i g h l y h o m o l o g o u s class I glycoprotein molecules synthesized by genes in the M H C and T l a regions. Soloski and co-authors argue that this similarity indicates that these loci arose from replicates of a primordial gene which susequently diverged to the present closely related forms. It is further argued that the presence of cell-surface structures resembling Q a and T L in the guinea pig and h u m a n suggests that the gene duplication events
occurred prior to speciation. While it is difficult to argue with the postulate of gene duplication, the precise timing of such a duplication may require further data. The murine M H C class I molecules have a number of species-specific residues in common, that is, residues which are present on all murine molecules but on no human class I M H C molecule. The existence of these residues would argue that certain of the duplication events occurred after divergence of the evolutionary pathways that led to the mouse and human. The effect of the common biochemical properties of the various class I molecules on the primary structure must also be considered before constructing detailed hypotheses. Each is a membrane glycoprotein and each binds 132-microglobulin in a non-covalent fashion. There are no extensive structural requirements for the addition of carbohydrate units and a number of different amino acid sequences appear equally to serve the function of membrane binding. The nature of the structure required to non-covalently bind ~2-microglobulin is at present obscure although there appears in each of the class I moleculesa domain (residues 181-270)with a highly conserved structure that bears some homology to the immunoglobulin constant region domain. It may be questioned whether a rigorous requirement for identity in this region with little homology in other domains would completely account for the results obtained in the peptide mapping studies. Thus, the high degree of similarity among the M H C and T l a class I antigens remains to be more completely defined and related to their respective functions. T. j. KINDT
Laboratory of hnmunogenetic.~, Natiorml lnslilule of Allergy and Infectious Diseases, Bethe~da, MD 2020,5, U.S.A.
References l Klein, J. (1975) in Biology of lke 3 louse /lislocompatibilil}, Complex New York, Springer-Verlag 2 Flaherty, L. (1980) in The Role of the Major Histocornpatibility Complex in Immunobiology (Doff, M.ed., in press) 3 Michaelson, J., Flaherty, L., Vitetta, E. and Poulik, M. (1977) J. Exp. Med. 245,1066 4 Stanton, T. H., Calkins, C. E., Jandinski, J., Schendel, J., Stutman, O., Cantor, H. and Boyse, E. A. (1978) J. Exp. Med. 148,963 5 Coligan, J. E., Kindt, T. J., Uehara, H., Martinko, J. and Nathenson, S. G. (1981) Nature (London) 291, 35-39 6 Soloski, M.J., Uhr, J. w., Flaherty, L. and Vitetta, E. S. (1981) J. Exp. Med. 153, 1080-1093
IgG heavy chain (Gin) allotypes in diabetes Considerable interest has been focussed on the genetic polymorphisms which control the immunoglobulin (Ig) allotypic determinants of the heavy chain and their possible associations with certain diseases which are believed to have an autoimmune basis. Although Elsevier/North-Holland Biomedical Press 1981 0167 - 4919/81/0000 - 0000/$02.50
there seems little doubt that the major genetic susceptibility to diseases such as Type 1 (insulindependent) diabetes, autoimmune thyroid disease, and Addison's disease is determined by genes in the H L A complex there are several facets of tile immuno-
immlmology loday, 5'eplember 19~W
genetic basis to these p r o b l e m s w h i c h r e m a i n unresolved. For example, the distribution of organspecific autoantibodies - ' c l a s s i c a l ' islet-ceil antibody, thyroid microsomal antibody and gastric parietal cell a n t i b o d y - in the nonaffected siblings of T y p e 1 diabetic p r o b a n d s is independent of the potential H L A genetic susceptibility, as j u d g e d by the H L A haplotype concordance with the p r o b a n d ~. In other words, if there is a genetic control of a u t o a n t i b o d y production, it is clearly separate from the genetic predisposition to pancreatic B-cell injury. I m m u n o g l o b u l i n allotypes have been investigated in a variety of populations indicating that certain G m haplotypes are particularly prevalent in Mongoloids and other ethnic groups 2. F r o m the evidence currently available, the G m locus is not on the short a r m of chromosome 6, although its exact location remains unknown. Most of the studies on G m allotypes and disease have been done in .Japan. Large numbers of serum samples from patients with various a u t o i m m u n e diseases have been investigated using a haemagglutination inhibition test on microflocculation slides employing officially recognized G m antiseraL~ The nine phenotypes observed in the J a p a n e s e p o p u l a t i o n could be assigned to four groups (Gml'21; Gml,2,2'; G m 1,13,15,1(' and GmI,:L~,I3). The G m 1,2,21 group was found in 36% of patients with myasthenia gravis compared with 16% of healthy controls (p
