Structural studies of immunoglobulins—II the varying susceptibility to papain-digestion of a group of human myeloma γG-globulins

Differential immunocytological expression of a paraprotein-associated idiotype is possibly related to variant immunoglobulin molecules in plasmacytoma cells

An anti-idiotype antibody (anti-Id Ab) was made by immunization of a rabbit with the IgG-2/lambda paraprotein from a plasmacytoma patient (Sa). The antibody was directed against determinants of heavy (H) and light (L) chains on the F(ab)2 piece of the paraprotein. Using this antibody an unusual pattern of cytoplasmic fluorescence was seen with bone marrow cells of the patient. One population (type I) showed reactivity in association with gamma and lambda chains, the other (type II) with the anti-Id Ab only. So, by immunological methods, biclonality could be demonstrated using the anti-Id Ab but not with anti-isotype antibodies. L chains of mol. wt 23.5 and 17.0 kd were observed. The H and L chains of small molecular weight were not detected in the patient's serum nor in the culture supernatant. Thus, deleted and intracellularly degraded H and L chains may cause the unusual staining pattern of the type II cells.

A new protocol to digest human IgM with papain that results in homogeneous Fab preparations that can be routinely crystallized

A method has been developed for the routine production of Fab fragments from human IgM in high yield. After the IgM is purified at physiological pH, it is digested with papain in the presence of cysteine at room temperature for 16 hours. The Fab fragments are purified initially by gel filtration and then by ion exchange chromatography. The yield of Fab has been 60-80%. Some heterogeneity in the size of the Fabs from the different monoclonal IgMs has been observed. Fab fragments from four different IgM rheumatoid factors (RF) have been crystallized after such digestion and purification, in a variety of conditions including phosphate buffer alone or with the precipitating agents ammonium sulfate, polyethylene glycol or methylpentanediol. This modified papain digestion method has also been used for another non-RF monoclonal human IgM with equally good yield. Biological activity can be detected in the purified Fab fragment indicating that this procedure does not destroy the native conformation of the molecule.

Heat sensitivity of porcine IgG

The sensitivity to heat of porcine IgG was studied. The serum from immunized pigs was heated at 56 degrees C for 30 min as for decomplementation. The elution pattern of the serum proteins on an agarose gel column showed a dramatic change with the appearance of a large peak of the gel-excluded material. This peak contained mainly IgG molecules which still retained its antibody activity. This fact points to misinterpretations which can easily occur in 7S and 19S antibody recognition during the porcine immune response. Correlation is suggested of this property with the large number of interheavy chain disulfide bridges present in porcine IgG.