Immunoglobulin A only weakly. IgA exists in two isotypes, IgA1 and IgA2. They are both heavily glycosylated proteins. While IgA1 predominates in serum (~80%), IgA2 percentages are higher in secretions than in serum (~35% in secretions); the ratio of IgA1 and IgA2 secreting cells varies in the different lymphoid tissues of the human body: Both IgA1 and IgA2 have been found in external secretions like colostrum, maternal milk, tears and saliva, where IgA2 is more prominent than in the blood. Polysaccharide antigens tend to induce more IgA2 than protein antigens. Both IgA1 and IgA2 can be in membrane-bound form. ("see B-cell receptor")
Invariant of a binary form the form itself of degree 1 and order 1. The algebra of invariants of the quadratic form "ax" + 2"bxy" + "cy" is a polynomial algebra in 1 variable generated by the discriminant "b" − "ac" of degree 2. The algebra of covariants is a polynomial algebra in 2 variables generated by the discriminant together with the form "f" itself (of degree 1 and order 2). The algebra of invariants of the cubic form "ax" + 3"bx""y" + 3"cxy" + "dy" is a polynomial algebra in 1 variable generated by the discriminant "D" = 3"b""c" + 6"abcd" − 4"b""d" −