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")
Sesquilinear form to is Similarly, is orthogonal to with respect to , written (or simply if can be inferred from the context), when . This relation need not be symmetric, i.e. does not imply (but see "" below). A sesquilinear form is reflexive if, for all , That is, a sesquilinear form is reflexive precisely when the derived orthogonality relation is symmetric. A -sesquilinear form is called -Hermitian if there exists such that, for all , If , the form is called -"Hermitian", and if , it is called -"anti-Hermitian". (When is implied, respectively simply "Hermitian" or "anti-Hermitian".) For a nonzero -Hermitian