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A 56 residue fragment derived from a Waldenströme IgM protein and consisting of 24 residues of the amino-terminal portion of the Cmu4 domain disulfide bonded to 32 residues of the carboxy-terminal region of the loop has been shown to fix active C1 (C1) in a C1-fixation assay. Cleavage of the disulfide bond within the CH4 fragment resulted in a marked decrease of C1-fixing ability, although the isolated A and B fragments did retain a limited ability to fix C1. Upon incubation with normal human serum the intact CH4 fragment and equal molar amounts of the isolated A and B peptides consumed C4 suggesting that the C1-activating determinant of IgM remains intact in these three fragments. Furthermore, on a molar basis the intact or the reduced CH4 fragment consumed C4 as effectively as each of its component chains suggesting that transient binding of C1 by the individual A and B peptide chains is sufficient to activate C1. On the basis of these observations it is proposed that a classical complement fixation function, i.e. C1 binding and activation, can be localized within a region of the IgM molecule corresponding to the Cmu4 domain.

Immunoglobulins and their respective heavy (H) and light (L) polypeptide chains from species representing the major classes of vertebrates were analyzed for their carbohydrate composition by gas chromatography of the alditol acetate derivatives of the monosaccharides released by acid hydrolysis. Mannose, galactose, glucosamine and sialic acid were present in the immunoglobulins from all the species investigated. Fucose however was absent from the immunoglobulins of two species of animals studied. Most of the carbohydrate was found associated with the H chains. The carbohydrate composition was felt to be heterogeneous in that the quantities of fucose and sialic acid found often accounted for less than one residue per H chain. Whereas species representative of the mammals and birds had mannose to galactose ratios greater than one, the ratio of these sugars to each other in the immunoglobulins from animals below the birds was on the order of one.

This preliminary study was undertaken to investigate the chemical nature of the Thy-1.2 antigen expressed on the murine cell line S-49.1 TB-2-3 (S-49). The presence of the Thy-1.2 antigen was indicated by the inhibition of AKR anti-C3-Thy-1.2 serum induced lysis of 51Cr-primed target cells. It was found that limited digestion of S-49 cells with crude papain yielded a Thy-1.2-containing solution. The protein nature of the Thy-1.2 antigen obtained in this manner was indicated by changes after proteolytic digestion. Separate digestions with crystalline papain, insolubilized papain, and insolubilized protease all destroyed the Thy-1.2 activity. These results suggest that the protein moiety is necessary for Thy-1.2 activity.

TL antigen was solubilized from the tumor ASLI (TL. 1,2,3) by papain digestion. The subfragments of 125I-labeled TL were examined by two methods. The first involved immune precipitation followed by electrophoresis on SDS-acrylamide gels. This treatment yielded three bands of molecular weight 39,000 and 19,000, as well as material which migrated with the tracking dye. In the second procedure the papain digested material was partially purified on Sephadex G-200. The active fraction from G-200 was labeled with 125Iodine, mixed with alloantiserum and rechromatographed on G-200. The isolated immune complexes were boiled in SDS and 2-mercaptoethanol, then separated on a SDS-Sephadex G-150 column. Two radioactive peaks were eluted indicating an absence of the 19,000 m.w. component following the latter method of purification.