“…The measurement of IgG4 levels seems to be of special clinical interest. Indeed, alterations in serum IgG4 levels have been observed in various primary immunodeficiency states, including ataxia-telangiectasia and selective IgA deficiency with frequent association with IgG2 defect and correlation with frequency of infections (Terry, 1968;Rivat et al, 1969;Schur et al, 1970;Yount et al, 1970;Natvig et al, 1971;Oxelius, 1974Oxelius, , 1979bYount, 1975;Morell et al, 1975;Rivat-Peran et al, 1981;Oxelius et al, 1981Oxelius et al, , 1982Lefranc et al, 1983;Ugazio et al, 1983), in atopic allergy (Parish, 1981;Merret et al, 1983), in malignant melanoma (Daveau et al, 1977) and in certain respiratory diseases (Van Nieuwkoop et al, 1982).…”