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")
Strophic form Strophic form Strophic form, also called verse-repeating or chorus form, is the term applied to songs in which all verses or stanzas of the text are sung to the same music. The opposite of strophic form, with new music written for every stanza, is called through-composed. The term is derived from the Greek word , "strophē", meaning "turn". It is the simplest and most durable of musical forms, extending a piece of music by repetition of a single formal section. This may be analyzed as "A A A...". This additive method is the musical analogue of repeated stanzas in poetry