SUPPRESSED G2M(N) LEVELS FROM IGHCG2 IN IGA DEFICIENCY

The aim of the study was to investigate the production of Ige from alt ernative alleles of IGHCG1, IGHCG2 and IGHCG3, closely related to IGHC A1 and IGHCA2 on chromosome 14, in IgA deficient (IgAD; serum IgA leve ls < 0.05 g/l) for individuals. Sixty-two IgAD individuals were includ ed in the study and sera were investigated with the sensitive competit ive indirect ELISA for measuring serum concentrations of the Gm alloty pes G1m(a), G1m(f), G2m(n) and C3m(b), performed with specific monoclo nal antisera and purified myeloma proteins in combination with IgG sub class quantitation. The known 'compensatorily increased' serum levels of IgG1 and IgG3 were recognized with significantly increased G1m(a) a nd G1m(f) from IGHCG1 and significantly increased G1m(g) and G3m(b) fr om IGHCG3. The quotients of G1m(a)/G1m(f) from IGHCG1 and G3m(g)/G3m(b ) from IGHCG3 were also normal. Instead, the levels of G2m(n) from IGH CG2 were selectively decreased in combination with normal or increased levels of G2m('') from the same IGHCG2. The quotient G2m(n)/C2m('') w as also significantly decreased. As the selectively decreased G2m(n) a llotype expression from IGHCG2 was situated close to the non-expressin g IGHCA1, the origin of most serum IgA could be the result of a defect ive common regulating factor. The selectively decreased G2m(n) allotyp e levels from IGHCG2 must also be discussed with a view to Gm allotype suppression described in mice. The selectively decreased G2m(n) allot ype levels in G2m(n,'') heterozygous IgAD individuals could be the res ult of a preferential allelic exclusion of G2m(n) favoring G2m('') on IGHCG2 in many cells.