Light chain sequences of human IgM cold agglutinins (variable-region subgroups amino-acid sequence-kappa light chain-N-terminal)

Molecular characterization of the variable domains of an ?IIb?3-specific immunoglobulin�M ? platelet cold agglutinin in a follicular lymphoma patient with treatment refractory autoimmune thrombocytopenia: idiotypic overlap between ?IIb?3 integrin antibodies

BACKGROUND

Cold hemagglutinins are generally immunoglobulin M (IgM) kappa antibodies reactive at temperatures below 37 degrees C and if of high titer may cause hemolysis. Platelet (PLT) cold agglutinins (CAs) are rare and poorly characterized. A detailed molecular characterization of the variable domains of a pathologic, PLT-reactive, CA is presented.

CASE REPORT

A 70-year-old woman was admitted with rectal bleeding accompanied by widespread petechiae, bruising, tongue and buccal mucosa bleeding, and epistaxes and proved refractory to HLA- and HPA-matched PLTs. Detailed investigation showed monoclonal heavy-chain gene rearrangement with an IgM paraprotein of 3.3 g per L and a trace of kappa Bence Jones protein in the urine, compatible with a diagnosis of secretory B-cell non-Hodgkin's lymphoma (B-NHL). PLT antibody (PAIg) investigations revealed a potent IgM kappa PLT CA. Sequencing of the rearranged variable domain genes of the malignant clone together with idiotype-specific antibodies obtained by DNA-based immunization of rabbits and matrix-assisted laser desorption/ionization-time-of-flight analysis of the PAIgM provided a irrefutable link between the thrombocytopenia, the IgM paraprotein, and the PAIgM against alphaIIbbeta3. The thrombocytopenia and bleeding were refractory to standard treatment and PLT transfusion, but treatment with rituximab resulted in a recovery of the PLT count and a complete remission of B-NHL.

CONCLUSION

The IgM kappa paraprotein derived from the malignant B-cell clone was a potent and clinically significant CA against alphaIIbbeta3. The testing for PLT CAs in patients with a paraprotein and refractory to matched PLTs may aid the selection of appropriate treatment.

Restriction in the repertoire of the immunoglobulin light chain subgroup in pathological cold agglutinins with anti-Pr specificity

BACKGROUND AND OBJECTIVES

In cold agglutinin disease, monoclonal red blood cell autoantibodies, termed cold agglutinins, induce haemolysis in patients exposed to the cold. Commonly, these autoantibodies are directed against the developmentally regulated I/i blood groups. A second blood group system, the Pr system (located on glycophorins), is involved less frequently. Anti-Pr cold agglutinins recognize either alpha 2,3- or alpha 2,6-linked N-acetylneuraminic acid as the immunodominant group. Cold agglutinins of anti-I/i specificity show a remarkable restriction in their genomic repertoire of the immunoglobulin heavy and light-chain immunoglobulin-variable domain (i.e. exclusive use of VH4-34 in heavy chains). For anti-Pr cold agglutinins, preliminary data on the repertoire of the light-chain variable domain indicate a preference for the subgroup Vkappa IV. To elucidate restrictions in the light-chain variable-domain subgroup repertoire of anti-Pr cold agglutinins systematically, and to discuss these results in the context of their anti-Pr(1-3) subclassification and immunodominant sialic acid, light chains in 13 anti-Pr cold agglutinins were investigated.

MATERIALS AND METHODS

The anti-Pr light chains were isolated using temperature-dependent absorption/elution techniques. Subsequently, they were subjected to N-terminal Edman degradation, and the light chain Vkappa subgroup was affiliated using the Kabat database.

RESULTS

Five of 13 (38%) light chains belonged to Vkappa IV, five of 13 (38%) to Vkappa I and three of 13 (23%) to Vkappa III. Anti-Pr with Vkappa IV subgroup light chains exclusively recognized alpha 2,3-linked N-acetylneuraminic acid.

CONCLUSIONS

Including data from the literature, the repertoire of the light-chain variable domain in pathological anti-Pr cold agglutinins exhibits a clear bias towards the use of the single germline gene-derived subgroup, Vkappa IV (eight of 17 or 47%). The association of Vkappa IV subgroup light chain-containing anti-Pr cold agglutinins with binding to alpha 2,3-, but not alpha 2,6-linked N-acetyneuraminic acid raises speculations about a possible role of subgroup-derived determinants in anti-Pr binding.

Molecular characterization of a cross-reactive idiotope on human immunoglobulins utilizing the VH4-21 gene segment

The anti-idiotypic (anti-Id) antibody (Ab) 9G4 binds a cross-reactive idiotope (CRI) present in a select group of human autoantibodies. This Id has been localized to the portion of immunoglobulin (Ig) heavy (H) chains encoded by the VH4-21 gene segment, a member of the human VH4 family. This gene segment is utilized by essentially all cold agglutinin (CA) Abs with I/i specificity isolated from patients with CA disease stemming from chronic lymphoproliferative disorders. In this study, mutational analysis of a CA has been used to determine the structural basis for 9G4 binding to Abs utilizing the VH4-21 gene segment. Recombinant CA H chain mutants were produced and their 9G4 reactivity determined. Mutants were generated by exchanging VH4-21 sequences in the FR1, CDR1, and CDR2 with corresponding sequences from a closely related gene segment V71-2, a VH4 family member that is associated neither with Abs having CA activity nor with Abs that react with 9G4. The results indicate that the motif AVY at amino acid positions 23-25 in FR1 defines the 9G4 idiotope. Reaction of these recombinant Abs with a polyclonal rabbit anti-CA antiserum absorbed to render it specific for a CA CRI also maps predominantly to FR1. These findings indicate that the solvent-exposed FR1 plays an important role in eliciting an immune response to Igs.

Expression of rheumatoid factor associated cross-reactive idiotopes by glandular B cells in Sjögren's syndrome

B cell expression of the germline gene-encoded, kappa IIIb-associated, rheumatoid factor (RF) cross-reactive idiotope (CRI) 17-109 and three VHI associated RF CRIs (G6, G8, H1) was investigated immunocytochemically in labial salivary glands from nine patients with primary and six with secondary Sjögren's syndrome, and in inflamed submandibular salivary glands from 10 patients with no history of connective tissue disease. Expression of CRIs by B cell infiltrates in labial glands from patients with primary and secondary Sjögren's syndrome were similar. Lymphoid infiltrates of labial glands from Sjögren's syndrome patients contained a higher proportion of kappa III+ cells reactive for the kappa IIIb-associated 17-109 idiotope (P less than 0.01) and larger G6 (P less than 0.02) and H1 (P less than 0.01) positive B cell populations than those within inflamed submandibular salivary glands. Furthermore, in labial glands there was a significant correlation between numbers of 17-109 and G6 idiotope reactive cells (r = 0.61; P less than 0.02), reflecting the known association between these H and L chain CRIs in RF IgM paraproteins. These results indicate that B cells bearing both VKIII and VHI-associated CRI are increased in the glandular infiltrates in Sjögren's syndrome and support the idea that this condition is associated with proliferation of immature B cell clones retaining germ-line V genes.

Autoantibodies and the fetal antibody repertoire

Developing fetal B cells preferentially rearrange a restricted subset of the encoded antibody gene segments. There are striking structural similarities between elements expressed early in man and in mouse, most evident on comparison of murine VH elements from the VH7183 family to human VH elements of the VH3 family. The similarity is pronounced in two framework regions which together encode a possible binding site that is distinct from the classical antigen-combining site. By comparing all known human and murine VH gene sequences, we have demonstrated that these regions have been conserved in a family-specific manner throughout the mammalian radiation. The "non-conserved" spacer of the recombinase recognition signal is also highly conserved in a family-specific manner, suggesting a mechanism by which the expression of family-dependent features may be regulated. The evidence that such features contribute to the high incidence of self- and poly-specificity in the fetal antibody repertoire is reviewed.

Autoantibody-associated kappa light chain variable region gene expressed in chronic lymphocytic leukemia with little or no somatic mutation. Implications for etiology and immunotherapy

Recently the minor B cell subpopulation that expresses the CD5 (Leu-1) antigen has been implicated as a source of IgM autoantibodies. Chronic lymphocytic leukemia (CLL), the most common leukemia in humans, represents a malignancy of small B lymphocytes that also express the CD5 antigen. However, little is known concerning the antibody variable region genes (V genes) that are used by these malignant CD5 B cells. We have found that a relatively high frequency of CLL patients have leukemic B cells with surface immunoglobulin (sIg) recognized by 17.109, a murine mAb specific for a kappa light chain associated crossreactive idiotype (CRI) associated with rheumatoid factor and other IgM autoantibodies. Flow cytometric analyses revealed that the relative expression of the 17.109-CRI by circulating leukemic B cells was directly proportional to the levels of sIg kappa light chain, indicating that there exists stable idiotype expression in the leukemic population. To examine this at the molecular level, the nucleic acid sequences encoding the Ig kappa light chains of two unrelated patients with CLL bearing sIg with the 17.109-CRI were determined. Analyses of multiple independent kappa light chain cDNA clones did not reveal any evidence for sequence heterogeneity in the CLL cell population. Furthermore, the nucleic acid sequences expressed by the leukemic cells of these two patients were identical or very homologous to a germline V kappa gene isolated from placental DNA, designated Humkv 325, or "V kappa RF" because of its association with IgM autoantibodies. This study suggests; (a) that the malignant CD5+ B lymphocytes in CLL use the same V kappa gene that has been highly associated with IgM autoantibodies and (b) that the expression of V genes is stable in CLL, in contrast to other B cell malignancies examined to date. We propose that many CLL cases represent malignancies of autoreactive CD5 B cells that use a restricted set of conserved V genes. This property may render CLL particularly amenable to immunotherapy with antiidiotypic antibodies.

Association between human IgM autoantibodies and kappa chain allotypes

The relationship between the immunoglobulin kappa light chain allotypes and autoantibodies was studied in a series of seven human monoclonal kappa-bearing IgM antibodies with Rheumatoid Factor (RF) activity, two IgM anti-low density lipoprotein (LDL) antibodies, and one IgM anti-intermediate filament (IF) antibody. Residues at amino acid positions 153 and 191 related to the Km allotypes in human kappa chains were determined by an HPLC tryptic fingerprint and corroborated by amino acid sequence analysis. All the autoantibodies shared similar variable regions derived from the V kappa IIIb gene(s). The seven RF and the anti-IF were associated with the Km(3) constant region allotype whereas the two anti-LDL were associated with the Km(1,2) allotype. Thus, monoclonal autoantibodies showed the same Km allotypic distribution as the normal population. However, although the number of samples is small, it seems likely that a preferential association may exist between particular V kappa genes and Km alleles in the generation of autoantibodies with different specificities.

Human rheumatoid factor crossidiotypes. II. Primary structure-dependent crossreactive idiotype, PSL2-CRI, present on Wa monoclonal rheumatoid factors is present on Bla and other IgM kappa monoclonal autoantibodies

The amino acid sequence of the L-CDR2 (complementarity-determining region) of Bla mRF (monoclonal rheumatoid factor) is identical to that of the Wa mRFs. The PSL2-CRI (crossreactive idiotype), as determined by anti-PSL2, which has been shown to be present on all Wa mRFs, is also present on the Bla mRF and other monoclonal autoantibodies. PSL2-CRI is, therefore, not unique to Wa mRFs and may be present on most IgM kappa monoclonal autoantibodies. Whether PSL2-CRI is a crossidiotype (XId) that is selectively present on autoantibodies or represents an allotypic marker for a V kappa III gene is undetermined.

The VKIIIb light chain sub-subgroup: restricted association with mu heavy chain in normal human serum

The VKIII human kappa light chain subgroup has been serologically and structurally divided into two sub-subgroups, VKIIIa and VKIIIb. VKIIIb has been shown by others to be strikingly prevalent in IgM autoantibodies, but no studies have been performed to determine heavy chain isotype association with VKIIIb light chain in normal human serum. The VKIIIb sub-subgroup was shown here to be associated with mu heavy chain in normal human serum, but was not detected in association with gamma or alpha heavy chain. Approximately 25 +/- 15% of IgM-kappa was determined to be VKIIIb. Both intact IgG and purified light chains from pooled IgG did not bind monoclonal anti-VKIIIb, indicating that the determinants recognized by anti-VKIIIb are not merely masked in intact IgG. These results are the first report of a light chain sub-subgroup showing preferential association with a heavy chain isotype.

Sequence similarities among kappa IIIb chains of monoclonal human IgM kappa autoantibodies

Light chains of the serologically and chemically defined V region sub-subgroup kappa IIIb are preferentially associated with several types of human IgM kappa (monoclonal) autoantibodies and are remarkably homologous in primary structure, as evidenced by partial amino acid sequence data. To establish the extent of homology among such proteins, we have determined the complete variable region (V) sequence of the light chains of four monoclonal IgM kappa autoantibodies, of which two (GAR and GOT) are rheumatoid factors (RFs), the third (SON) has anti-apo beta lipoprotein specificity, and the fourth (PIE) binds specifically to intermediate filaments. The region encoded by the V kappa segment gene (positions 1-95) in all four light (L) chains is virtually identical in sequence, differing by only one residue in the FR3 of protein SON and in the first CDR of protein GOT. Further, the CDR3 of kappa chain SON contains an additional residue (prolyl) located at the carboxyl-terminus of the V segment. The region encoded by the J gene (positions 96-108) is identical after position 96 for the two RFs GAR and GOT (J kappa 2), but different in proteins SON (J kappa 4) and PIE (J kappa 1). The amino acid residue at position 96, located in CDR3 at the site of combinatoriaL joining of the V kappa and J kappa gene segments and involved as a contacting residue in the hapten binding site, is different in all four light chains. These results demonstrate the extensive homology in sequence among light chains of IgM kappa autoantibodies and indicate that a particular V kappa germ line gene, kappa IIIb, is expressed as a phylogenetic response to certain self antigens or as part of a selection process by which these autoimmune responses are regulated.

Complete amino acid sequence of variable domains from two monoclonal human anti-gamma globulins of the Wa cross-idiotypic group: suggestion that the J segments are involved in the structural correlate of the idiotype

The complete amino acid sequences of the variable regions of two human IgM anti-gamma globulins are reported. The two proteins, Sie and Wol, share idiotypic determinants that are distinct from those shared by the two previously sequenced IgM anti-gamma globulins, Lay and Pom [Capra, J. D. & Kehoe, J. M. (1974) Proc. Natl. Acad. Sci. USA 71, 4032-4036; Klapper, D. G. & Capra, J. D. (1976) Ann. Immunol. (Inst. Pasteur) 127C, 261-271.] In contrast to Lay and Pom, Sie and Wol have very little homology in the complementarity-determining hypervariable regions of either their light or heavy polypeptide chains. However, there are only two amino acid differences in the framework portions of the light chains, and the J segments of both chains are homologous. These data suggest that the predominant idiotypic determinant in this cross-idiotypic system may be different than in the Po group and may be either related to their light chain framework structures or to the amino acid sequence in the J segments of these molecules.

Variable-region subgroup and specificity of cold agglutinins

The variable-region subgroup determined by amino acid sequence analysis of heavy and light chains of two monoclonal cold agglutinins with the new anti-Gd specificity is reported. Both proteins belong to the VHIII subgroup of heavy chains; one light chain falls into the V kappaI subgroup, the other has a blocked N-terminus which so far has not been observed in human kappa chains. The comparison of anti-Gd with anti-I/-i or anti-Pr cold agglutinins indicates that anti-Gd differs from other cold agglutinins with respect to variable-region subgroup. The data extend previous findings on the restriction of certain antibodies to distinct variable-region subgroups.

Actual aspects of cold agglutination

Cold agglutinins (CA) can be directed against antigens of the I/i system and the Pr complex. In addition, anti-Gd CA have been recently described. The CA immunoglobulins, serological specificities and the antigen immunochemistry are reviewed. CA permitted studies on interrelations between antibody structures and specificities. The significance of subgroup preferences and cross-idiotypic specificities is discussed. Interrelations between CA specificities and certain virus infections are pointed out, and recent results obtained from studies using CA as indicators for membrane alterations of other than red cells are reviewed.

Some correlations between specificity and sequence of the first complementarity-determining segments of human kappa light chains

Examination of the sequences of the first complementarity-determining segments of the light chains of two IgM cold agglutinins agains blood group I, four monoclonal IgM antibodies against IgG proteins, and of three Bence Jones proteins provides clues for predicting which residues contribute to antibody specificity and indicates that these predictions may be tested by evaluating recovery of antibody activity and specificity when various light chains are recombined with homologous and heterologous heavy chains.

Serological detection of variable region (Vh) subgroups of Ig heavy chains

Serological test systems were established for determining the heavy-chain variable region (Vh) subgroups of immunoglobulin heavy chains. Myeloma proteins with known Vh subgroups based on amino acid sequence were utilized as the primary basis of reference for analysis by hemagglutination and hemagglutination inhibition. Good agreement between the chemical and serological typing was obtained and nonoverlapping systems established for the three major Vh subgroups. In a survey of 167 myeloma proteins, all except two were exclusively positive in one of the three systems. The two exceptions may represent a fourth subgroup. There was an overall incidence ratio of 1:2:3 for VhI:VhII:VhIII subgroups. Some differences in the overall ratios were encountered within the immunoglobulin classes. Certain advantages of the serological typing antisera were discussed with special emphasis on their use for studies of Vh antigens on the membranes of lymphocytes.

Structural studies of induced antibodies with defined idiotypic specificities. IV. The heavy chains of anti-streptococcal group A carbohydrate antibodies from Sprague-Dawley rats carrying a cross-reacting idiotype

The heavy (H) chains of three anti-streptococcal group A carbohydrate antibodies (anti-SACHO) of restricted heterogeneity, elicited in inbred Sprague-Dawley rats, were subjected to 40 cycles of automated Edman degradation. All three antibody H-chain preparations had an identical amino acid sequence and were classified as a variant of the VHIII subgroup of immunoglobulin H chains. A comparison of the H-chain sequence of these antibodies with that of pooled rat gamma chains suggests that a very minor population of H chains (closely related to the VHIII subgroup) has been 'recruited' as a consequence of this immunization. This observation further supports the notion that 'framework' and 'specificity' or 'hypervariable regions' are closely linked.

Kappa chain (V kappa III) subgroup-related activity in an idiotypic anti-cold agglutinin serum

In a search for H- or L-chain-related cross-idiotypic specificity among human anti-I and anti-i cold agglutinins, two idiotypic antisera raised against the IgMkappa cold agglutinin Da were tested for their binding activity to isolated cold agglutinin H and L chains. Negligible H-chain binding activity was found, but there was high-titre L-chain binding activity in one of the antisera. This was an unsuspected VkappaIII subgroup activity which enabled the classification of VkappaIII proteins into three subgroups. The kappa chains of five out of six anti-I and anti-i cold agglutinins belonged to the antigenically most active VkappaIII subgroup. Absorption of the idiotypic antiserum with a Bence Jones protein of this latter subgroup did not appreciably alter the precipitating cross-idiotypic activity of the antiserum when tested with intect cold agglutinins. However, these studies do not rule out the possible existence of a VkappaIII subgroup-associated conformational antigen in an intact Fab region, which is seen as a 'cross idiotypic' antigen by heterologous (rabbit anti-human) antisera.

Kappa-chain deficiency. An immunoglobulin disorder

Since kappa-chain deficiency is an unusual condition, we studied the clinical and laboratory findings in a patient with this deficiency. The patient had cystic fibrosis with concurrent malabsorption, diabetes mellitus and IgA deficiency. The serum levels of IgM and IgG were 0.85 and 7.22 mg per milliliter, respectively. Kappa type IgM and IgG was not present in serum and external secretions; gamma, mu and lambda chains were probably polyclonal in character. Antibodies against kappa chains were not detected in either the patient or the mother. Plasma cells containing kappa-type immunoglobulins were absent in jejunum samples and bone marrow; kappa-chainbearing B lymphocytes could not be detected in blood and bone marrow. The serum of one of the patient's sisters contained trace amounts of kappa-type immunoglobulins. The patient displays a complete absence of kappa-type immunoglobulins, probably owing to a genetic defect.

Clonal nature of the immune response to phosphorylcholine (PC). V. Cross-idiotypic specificity among heavy chains of murine anti-PC antibodies and PC-binding myeloma proteins

Seven mouse myeloma proteins with specificity for phosphorylcholine (PC) were found to share a common antigenic determinant. This group of proteins contained members which differed in genetic origin, heavy chain class, kappa-chain subgroup, individual antigenic determinants and specificity for choline analogues. The cross-idiotypic determinant, VH-PC, was antigenically similar in each of the proteins and was associated with the variable portion of the heavy chain in the region of the antibody combining site. Further studies showed that an indistinguishable determinant was present on IgM anti-PC antibodies isolated from all strains of mice tested regardless of histocompatibility or heavy chain allotype. In view of the finding that this cross-idiotypic determinant was not found on antibodies or myeloma proteins which lacked specificity for PC, the data strongly suggest that a particular heavy chain variable region has been preserved in all mouse antibodies with specificity for PC.

A common idiotype on human macroglobulins with anti-I and anti-i specificity

The reactions of an idiotypic antiserum prepared against an anti-I cold agglutinin (Da) were studied in radioimmunoassays which were designed to detect partial rather than complete idiotypic cross-reactions among cold agglutinins with anti-I and anti-i activity. Proteins showing strong idiotypic cross-reactions by gel precipitation could not inhibit the binding of 125I-labelled Da to anti-Da (individual specificity). It was necessary to use 125I-labelled cross-reactive proteins in order to demonstrate cross-idiotypic specificity and even the choice of the reference cross-reactive protein was important. The use of the 125I-labelled Fab fragment of a cross-reactive anti-I cold agglutinin (Low) allowed the detection of an idiotypic determinant common to at least 73% of cold agglutinins with specificity for the I-i antigen complex. Among these were two transiently occurring cold agglutinins following M. pneumoniae infection and infectious mononucleosis. This idiotypic determinant was not detected on cold agglutinins with anti-Pr specificity or on isolated monoclonal IgM or IgG lacking cold agglutinin activity, but it was present in low concentrations in pooled IgG. The common idiotypic determinant was found on IgM kappa cold agglutinins belonging to different VK subgroups and on an IgM lambda protein. A knowledge of the structural basis of such idiotypic cross-reactions among proteins from unrelated individuals should provide important information about the genes controlling the synthesis of site-related regions of antibodies.

Studies on the specificities of two IgM lambda cold agglutinins

The reactions of two monoclonal IgM lambda cold agglutinins, Sch and Sher, have been studied in detail with human and animal erythrocyte antigens. Although they were unusual in having lambda and not kappa polypeptide chains, they could be assigned to the anti I and anti-Pr₁ groups of cold agglutinins.

The findings with serum Sher indicated that the Pr₁ antigen may be more complex than previously thought. The occurrence of unexpectedly large numbers of specificities among monoclonal anti-I, anti-i and anti-Pr antibodies is discussed and it is suggested that each monoclonal antibody may recognize only a limited portion of a complex red cell antigen.

Cross idiotypic specificity among cold agglutinins in relation to combining activity for blood group-related antigens

The previous observations of cross idiotypic specificity of IgM cold agglutinins were further investigated in quantitative precipitin assays and attempts were made to relate shared idiotypic specificity to combining specificity for I, i and Pr antigens of red cells. Shared idiotypic determinants were observed among anti-I and anti-i antibodies which are now known to have combining specificity for determinants present on precursors of the ABH and Lewis blood group substances. There was evidence that one cold agglutinin, Ma, which had previously been shown to have an unusual kind of I specificity was deficient in the idiotypic determinants associated with the other anti-I proteins.

Anti-Pr cold agglutinins, which have specificities unrelated to I-i antigens, were found to have distinct cross idiotypic determinants which were not detected on anti-I and anti-i antibodies. IgA and IgM antibodies with Pr specificity isolated from different individuals were found to share idiotypic determinants.

Cross specificity antigens were detected at low concentrations in preparations of normal IgG and IgM, but not in any isolated monoclonal macroglobulins lacking cold agglutinin activity.

Clonal nature of the immune response to phosphorylcholine. IV. Idiotypic uniformity of binding site-associated antigenic determinants among mouse antiphosphorylcholine antibodies

A new idiotypic determinant(s) on mouse anti-PC antibodies is described. Antibodies to the determinant(s) were raised in rabbits by immunization with HOPC 8, a PC-binding myeloma protein, and were isolated from HOPC 8 immunoadsorbent by elution with PC. These antibodies react with binding site determinants on anti-PC antibodies raised in all 15 inbred mouse strains tested regardless of histocompatibility or allotype, but fail to react with antibodies of other specificities or with anti-PC antibodies raised in other rodent species. These results correlate closely with other studies which show similar binding specificity of anti-PC antibodies raised in 17 different strains of mice. The site-associated idiotypic determinant(s) is clearly distinct from that detected by mouse anti-HOPC 8 antisera. This latter determinant(s) is present on anti-PC antibodies of only a few strains of mice and may not be in the binding site.

Amino acid sequence of the N-terminal 139 residues of light chain derived from a homogeneous rabbit antibody

The amino acid sequence of the N-terminal 139 residues of the L (light) chain derived from a homogeneous rabbit antibody (designated BS-1) to type III pneumococci was determined. A combination of methods involving tryptic cleavage restricted to the 2 arginine residues of the molecule and mild acid hydrolysis of a labile peptide bond between the V (variable) and C (constant) regions of the L chain (Fraser et al., 1972) allowed the isolation of two large peptides comprising the entire V region (residues 1-109); these peptides were suitable for automated Edman degradation. The complete sequence analysis of the V region was carried out with only 4mumol of L chain. This material was homogeneous, although minor variant sequences, if present at the 10% value, would not have been detected. The L chain contains 3 intrachain disulphide bridges, whose pairing was established by diagonal electrophoresis: there is one V-region bridge between positions 23 and 88 and one C-region bridge between positions 134 and 194; the third one connects V and C domains between positions 80 and 171. When compared with the basic sequence of human kappa chains, rabbit L chain BS-1 appears to be more similar to the V(KI) prototype sequence than to V(KII) or V(KIII) sequences, where V(KI), V(KII) and V(KIII) represent subgroups I, II and III respectively of V regions of kappa light chains. The V regions of rabbit heavy and light chains are homologous to each other. The presence of two clusters of 3 glycine residues in positions 94-96 and 99-101 respectively is remarkable. Residues 94-96 may be related to antibody complementarity whereas residues 99-101 function probably as a pivot permitting the combining region of the L chain to make optimal contact with the antigenic determinant (Wu & Kabat, 1970).

Similarities in the light chains of anti-gamma-globulins showing cross-idiotypic specificities

A marked homogeneity of the light chains was observed in an analysis of 17 IgM proteins with anti-gamma-globulin activity. The V region subgroups of the light chains were determined by both sequence and antigenic analysis. The latter procedure permitted large scale screening for comparisons with control proteins. The two methods showed general agreement in the determination of Kappa III proteins; all proteins positive by antigenic analysis were also positive by sequence but exceptions were noted in the opposite direction. The anti-gamma-globulins showed by antigenic analysis a 92% incidence of VK III light chains as compared to an incidence of 27% among 81 control proteins without this activity. A similar selection was observed for an antigen (VK III b) which subdivided the kappa III proteins. The major Wa group of anti-gamma-globulins which had been delineated previously on the basis of cross-idiotypic specificity was primarily responsible for the special light-chain selection. All the proteins of this group contain VK III light chains and all were of the VK III b type. Current evidence indicates that additional light-chain similarities were involved in the cross-idiotypic specificity of the Wa group. It thus appears that for the anti-gamma-globulins various levels of selection of light chains are manifest ranging from a preponderance of kappa type, of kappa III subgroup, of kappa III b sub-subgroup and perhaps of still further subdivisions to account for the cross-idiotypic specificity.

Six BALB-c IgA myeloma proteins that bind beta-(1-6)-D-galactan. Partial amino acid sequences and idiotypes

Six IgA myeloma proteins of BALB/c origin which bind antigens containing beta-(1 --> 6)-D-galactan side chains have been isolated by affinity chromatography on galactoside-BSA-Sepharose columns. Partial amino acid sequences of of the light chains to residue Cys23 and the heavy chains to reside 30 were determined on the automated sequencer. No differences were found among the six V(K) sequences. Among some 50 partial V(K) sequences that have thus far been determined these six chains are the only ones thus far identified in this subgroup; at least 25 V(K) subgroups in the mouse have been identified so far. The heavy chain partial sequences were also very closely related but two differences were found. One protein differed from the other five by having isoleucine instead of leucine at position 5, a second protein differed from the others by having an unidentified amino acid at position 19. Using the highly sensitive inhibition of hemagglutination method it was found that each of the proteins possessed a unique inidividual antigenic determinant.

Evidence for modification of protein phosphorylation by cytokinins

Kinetin stimulated phosphorylation of protein in floated Chinese-cabbage leaf discs, but inhibited protein phosphorylation in nuclei+chloroplast extracts from Chinese-cabbage or tobacco leaves. Kinetin also inhibited protein phosphorylation in isolated tobacco nuclei or nuclei from carrot secondary-phloem tissue. Purified Chinese-cabbage leaf ribosomes exhibited protein kinase activity which was inhibited by kinetin and zeatin. The ribosome-associated kinase responded to kinetin and zeatin differently from that associated with nuclei+chloroplast preparations. Protein phosphorylation in vitro was not affected by adenosine 3':5'-cyclic monophosphate, indol-3-ylacetic acid or gibberellic acid. It was only inhibited by N(9)-unsubstituted purines, among which the known cytokinins were the most effective inhibitors. The results are discussed in relation to possible similarities between the effects of cytokinins in plant tissues and the effects of adenosine 3':5'-cyclic monophosphate in animal tissues. Both compounds appear to modify the activity of protein kinases and both affect many different cellular processes.

Sequence relationships among the variable regions of immunoglobulin heavy chains from various mammalian species

Immunoglobulin heavy chains of myeloma proteins from dogs and cata have been subjected to automated sequence analysis. When the results were compared with human heavy-chain sequences, all the dog and cat proteins could be unequivocally assigned to the V(H)III subgroup. This pattern contrasts with that in human proteins in which only 25% of all heavy chains sequenced belong to this subgroup. The 30 residues at the NH(2) termini of dog, cat, and human heavy chains had sequence identities near or exceeding 90%, in contrast to established interspecies sequence homologies of constant regions of about 60%. Some genes of the immunoglobulin heavy-chain variable region thus appear to have been conserved through a considerable period of evolutionary time. The analyses also showed that the presence of certain amino acids at certain positions in these heavy chains could be correlated with the species of origin. The occurrence of such "phylogenetically associated" residues is most consistent with the presence of a restricted number of genes in the heavy-chain variable region pool.