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The variability due to age and sex and the reciprocal relations of serum IgG, IgA, IgM, C3, C4, total cholesterol (TC), HDL-cholesterol (HDL-C) and triglycerides (TG) were studied in 87 subjects (46 men and 41 women, aged 20-75 years) selected for the absence of significant atherosclerotic lesions. Serum IgA and C3 were higher in men than in women (P less than 0.05) mainly in the age group 41-60, while IgM and HDL-C were higher in women than in men (P less than 0.05 and P less than 0.01, respectively), especially in the age group 20-40. Direct univariate correlations with age were found for serum TC (P less than 0.0001), IgA (P less than 0.001), and C4 (P less than 0.01) but the latter correlations was confirmed only in women by multivariate analysis. These 3 variables had the major increment in the age group 41-60 in men, while in women the increase associated with age was more progressive or late. Univariate analysis showed a 'ring' of highly significant correlations (P less than 0.0001) involving serum lipids and complement components (TC-C4-C3-TG-TC). The correlation between TC and C4 was present only in men in multivariate analysis and improved with increasing age. These findings might represent a clue to explain the previously reported association between serum C4 and atherosclerosis.

The presence of antibodies of the IgA class against dietary antigens (bovine IgG (BGG), beta-lactoglobulin, casein, alpha-lactalbumin and xanthine oxidase, chicken ovalbumin and crude gliadin) was checked in the sera of 23 severely atherosclerotic subjects (ATS) and 20 highly selected controls (C). In these subjects an association between serum IgA levels and atherosclerosis had previously been shown. Determinations were performed by a micro-ELISA method and results were expressed as absorbances at 405 nm x 1000. Higher levels of IgA antibodies were found in ATS with respect to C against beta-lactoglobulin (respectively, 113.4 +/- 152.4 (1 SD) vs. 40.0 +/- 34.2; P less than 0.005) and casein (69.8 +/- 35.5 vs. 52.4 +/- 27.5; P less than 0.05). There was no difference in IgG and IgM against these 2 proteins between the 2 groups. Significant differences of prevalence of IgA antibodies were found for the following antigens: beta-lactoglobulin (4 C and 16 ATS over the limit value of 51; P less than 0.002), xanthine oxidase (1 C and 9 ATS over 289; P less than 0.01), BGG (7 C and 17 ATS over 87; P less than 0.02) and casein (5 C and 14 ATS over 60; P less than 0.02). These data suggest an association between anti-milk IgA antibodies and atherosclerosis. Its relevance and significance deserves further investigation.