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")
Positive form a unique connection preserving the Hermitian structure and satisfying This connection is called "the Chern connection". The curvature formula_16 of a Chern connection is always a purely imaginary (1,1)-form. A line bundle "L" is called "positive" if is a positive definite (1,1)-form. The Kodaira embedding theorem claims that a positive line bundle is ample, and conversely, any ample line bundle admits a Hermitian metric with formula_17 positive. Positive (1,1)-forms on "M" form a convex cone. When "M" is a compact complex surface, formula_19, this cone is self-dual, with respect to the Poincaré pairing :formula_20 For "(p, p)"-forms, where formula_21, there