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")
Polar form of the Dirac equation formula_11 vanish simultaneously, the spinor field is called regular, and in this case it is always possible to find a local frame in which the regular spinor field acquire the form up to a transformation of the type formula_15 and up to the reversal of the third axis. Therefore, a regular spinor can, in general, be written according to where formula_17 is called module and formula_18 is called Yvon-Takabayashi angle, and where formula_19 is the generic complex representations of the Lorentz transformation that is needed to obtain the generic spinor in its most reduced form as is written above. When