Myeloma proteins with antibody activity

Vn. AFFINITY LABELING OF ANTIBODY MOLECULES OR MYELOMA PROTEINS WITH ANTIBODY ACTIVITY... 

D. Affinity Labeling of Myeloma Proteins with Antibody Activity... 

Mouse Myeloma Proteins with Antibody Activity against Antigens IN THE Environment of the Mouse"... 

Myeloma proteins with antibody activity generally possess one combining site per Fab fragment. 

Myeloma proteins with antibody activity have in some instances been found to share idiotypic specificity and amino acid sequence with induced antibodies reactive against the same antigen. This is perhaps the strongest evidence for the essential identity of myeloma proteins and antibodies. 

This is illustrated by the data in Table 2.6. Thus, when a = 0.7, a typical value, 25% of the combining sites have K values greater than 6 and less than KJ6-, the other 75% of the sites fall within the range, Kol6 to 6Kq. For a homogeneous population of combining sites, such as may be associated with a myeloma protein having antibody activity, a = 1 and the equation becomes... 

Not all BALB/c myeloma proteins with antiphosphorylcholine activity are similar. Some (MOPC 167, MOPC 603) do not share idio-type with other proteins having the same antibody activity and have L chains belonging to unrelated subgroups. The same principle applies to a myeloma protein with mti-Salmonella activity, MOPC 467, whose L chains differ from those of proteins 870 and 384. 

Eisen, H.N., Simms, E.S., Potter, M. (1968). Mouse myeloma proteins with antihapten antibody activity. The protein produced by plasma cell tumor MOPC-315. Biochemistry 7, 4126-4134. 

Many of the myeloma proteins exhibit antibody-like activity and some react selectively with carbohydrate antigens [74], Myeloma proteins which are reported to be homogeneous in molecular structure have been used extensively for elucidating the structure of different types of immunoglobulins [11, 12]. A myeloma protein preparation from ascitic fluid... 

The effective size of the active site of the myeloma protein with anti-levan activity appeared to be somewhat smaller. A trimer of the basic subunit of levan, fructose, showed maximum inhibitory capacity on a molar basis. The similarity in the type of specificity noted in myeloma proteins and in induced antibody provides one type of evidence for the concept that myeloma proteins have all the properties of induced antibodies. 

The method is also capable of differentiating among different antibody populations with the same specificity. Mouse anti-Dnp antibodies elicited by immunization with Dnp derivatives induce circular dichroic patterns, upon interaction with e-Dnp-lysine, that are strikingly different from those induced by MOPC 315, a mouse IgA myeloma protein with anti-Dnp activity (38). It was concluded that the combining site of protein 315 must differ in its fine structure from that of the majority of induced mouse anti-Dnp antibodies. 

With the exception of a myeloma protein with anti-Dnp activity, preparations used for these studies have been specifically purified antihapten antibodies, which are heterogeneous. The velocity constants reported, as well as equilibrium constants, are therefore average values. 

Table 2.5 summarizes data obtained with a number of haptens and their corresponding antibodies. Except for protein 315, a mouse myeloma protein with anti-Dnp activity, specifically purified rabbit antibodies were used. The data on reaction rates are expressed in terms of a second-order velocity constant, k, where the forward reaction velocity is V = A i2(A) (L) v is in mole/liter/second (A) and (L) are the molar concentrations of free (unoccupied) antibody combining sites and of ligand, respectively. The units of ki2 are 1/mole/second (M sec ). In measuring rates it is essential to have a method for detection of the product at a low concentration, since the concentrations of reactants must be sufficiently small so that the velocity of the reaction is not too rapid to measure. 

All preparations are specifically purified rabbit antibodies except for protein 315, which is a mouse myeloma protein with anti-Dnp activity. 

The frequent appearance of mouse myeloma proteins with antiphosphorylcholine or anti-Salmonella activity may possibly be ascribed to antigenic stimulation, resulting in the presence of substantial numbers of cells making antibody with these specificities and subject to malignant transformation. This implies that the transformation can occur subsequent to magnification of the clone after exposure to antigen. 

The known antigenic activity and suspected natural antigenic source are given. For some antigens, e.g., phosphorylcholine, a(l — 3)dextran, and /3(1 — 6)-D-galactan a number of myeloma proteins with the same specific antibody activity have been identified. Table adapted from Potter (86). 

XIV. SUMMARY OF EVIDENCE RELATING MYELOMA PROTEINS WITH SPECIFIC BINDING ACTIVITY TO INDUCED ANTIBODIES... 

In the same investigation (55) it was found that an IgM myeloma protein with Xo chains and anti-a(l — 3)dextran activity had all the idiotypic determinants of an IgA (Xo) protein with the same activity, but that relatively high concentrations of the IgM protein were required to inhibit binding of the IgA protein to its antiidiotypic antibodies. This result suggested that the Vh regions of the proteins may be similar but not identical. 

Subsequently, the region of the antibody-combining site was found to be a significant idiotypic determinant in a number of immunoglobulins, including myeloma proteins with activity against Dnp (94,95), phosphorylcholine (96) or dextran (55). 

Myeloma proteins occur in animal tumors of various types. The synthesis of these proteins can be induced in some experimental animals by injection of mineral oil, or the implantation of plastic discs.161 Myeloma proteins were shown to possess antibody activity, with specificity for different types of substances.161 Some of these proteins were found to combine with such carbohydrates as bacterial, cell-wall polysaccharides, lipopolysaccharides, dextrans, levans, and galactans.162 Myeloma proteins that combine with galactans or dextrans possess anti-galactan activity,163,164 or anti-dextran activity,165-167 and have been studied most extensively. 

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