Biosynthesis of Immunoglobulins

Myelomas are tumors of plasma cells and are excellent tissues for studying the biosynthesis and secretion of immunoglobulins. Many different lines of mouse myeloma cells are now available and some of these lines have been used for the study of carbohydrate attachment 

Uhr and co-workers (Moroz and Uhr, 1967 Schenkein and Uhr, 1970a,b Uhr and Schenkein, 1970 Zagury et al., 1970 Sherr and Uhr, 1969, 1970) have studied mouse plasma cell tumors which secrete IgG  

As mentioned above, the mouse myeloma cells studied by Uhr s group incorporate radioactive carbohydrate almost exclusively into IgG when radioactive leucine is used as a label, 50% of the intracellular protein-bound radioactivity and all of the secreted protein-bound label is due to IgG (Zagury et al., 1970). Radioautographic studies using the electron microscope were therefore performed on mouse myeloma cells at various times after labeling with tritiated leucine, galactose, and glucosamine, re- 

Melchers and Knopf (1967) have studied a mouse myeloma line (MOPC 46) which synthesizes and secretes not intact IgG, as do the 

Schubert (1970) has studied the incorporation of carbohydrate into immunoglobulin by two mouse myeloma lines which secrete IgM and IgA, respectively. Results were similar for these two lines and showed the presence in each tumor line of two types of intracellular heavy chain one of these types contained covalently linked carbohydrate, while the other type was carbohydiate-free. Only the carbohydrate-containing heavy chain was secreted, indicating once again a possible role for carbohydrate in the secretory process Sdiubert, however, also points out that many light chains are secreted, although they contain absolutely no carbohydrate. Neither cell line studied by Schubert (1970) incorporated carbohydrate into polyribosome-bound heavy chain, i.e., all carbohydrate is added after release of heavy chains from the polyribosomes on which 

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Williamson, A. R., and B. A. Askonas. 1967. Biosynthesis of immunoglobulins the separate classes of polyribosomes synthesizing heavy and light chains. J. Molec. Biol., 23 201-215. 

The rate of biosynthesis of immunoglobulins in chickens, per unit body weight, is comparable to that observed in man. The half-lives of chicken IgM and IgG are 1.7 and 4.1 days, respectively, values one-third and one-fifth of those of the corresponding human proteins (90,91). 

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