Identification of Rat Erythrocyte Antigens with a New Non-Radioactive Immunoprecipitation Technique

In order to examine how rat erythrocytes stimulate erythrocyte autoantibody production at the molecular level, we have identified rat erythrocyte antigens by immunoprecipitation and western blotting using monoclonal antibodies and antisera. A novel non-radioactive immunoprecipitation technique was used, which employed biotin as a label and a luminescent detection system. The new method was validated by comparison with conventional immunoprecipitation using 125I. Glycophorins of relative molecular mass (Mr) 81,000 and 38,000 were found to be the major antigenic components of rat erythrocytes, while band 3 (the most abundant erythrocyte membrane protein) was not recognized by rat-specific antibodies. The same surface antigens were recognized by sera from mice producing erythrocyte autoantibodies and by sera from mice in which autoantibody production was suppressed. Nine other minor rat-specific antigens were identified by blotting, ranging in Mr from 23,000 to 147,000. Analysis of the integral membrane proteins of rat and mouse erythrocytes by sodium dodecyl sulphate (SDS) electrophoresis followed by silver or periodic acid-Schiff (PAS) stains revealed differences between the glycophorins, but not between rat and mouse band 3. Thus, the major antigenic differences correspond to discernible biochemical differences between rat and mouse erythrocyte sialoglycoproteins.     

Monoclonal antibodies to human erythrocytes

Eight monoclonal antibodies from mouse hybridomas raised to normal human erythrocytes were tested with a panel of null-type erythrocytes, enzyme-treated normal cells, and by inhibition with human erythrocyte sialoglycoproteins. Two antibodies reacted poorly or not at all with RhNULL cells. These antibodies are of considerable interest since it may be possible to use them to elucidate the chemical nature of the antigens of the Rhesus blood group system. Four other antibodies were inhibited by sialoglycoprotein preparations. The antigens recognized were, respectively, two different determinants on the major sialoglycoprotein alpha (glycophorin A) and one determinant which is probably common to sialoglycoproteins alpha and delta (glycophorins A and B). Another antibody had anti-Wrb specificity. One of these antibodies is of considerable potential value for the further characterization of erythrocyte sialoglycoproteins.     

Anti-mouse red blood cell monoclonal antibodies use functionally rearranged genes from the VH J558 family and are derived from the CD5- B-lymphocyte subpopulation.

Autoimmune haemolytic anaemia (AIHA) can be induced in mice by repeated injections with rat red blood cells (RBC). Here we describe the identification of murine RBC autoantigens and cross-reactive rat antigens. Sera and RBC eluates from the AIHA-positive mice immunoprecipitated a murine RBC autoantigen of 42,000 MW that comigrates with a zone of glycophorin in PAS-stained polyacrylamide gels. In addition, the eluates immunoprecipitated a 105,000 MW protein corresponding to band 3, the erythrocyte anion channel, and two further components of 34,000 and 29,000 MW within the glycophorin zone. The 42,000 MW band was not detected by immunoblotting, indicating that it bears autoantigenic epitope(s) that are denatured during electrophoresis. Cross-reactive autoantibody in the eluates immunoprecipitated a rat RBC protein that comigrated with band 3, together with two bands of 36,000 MW and 34,000 MW that may represent minor rat glycophorins. In contrast, rat-specific serum IgG from mice with AIHA reacted predominantly with major rat glycophorins of 75,000 MW and 38,000 MW. Immunoblotting revealed that normal murine sera contain IgG that binds autologous spectrin from the RBC membrane skeleton, and that this activity is increased in mice with AIHA. Sera from AIHA-positive mice also reacted with other internal murine RBC components that are not exposed on the surface of intact cells. It is evident from the data that immunization of mice with rat RBC results in the generation of multiple autoantibodies with a complex range of specificities.     

Electrophoretic analysis of erythrocyte membrane proteins and glycoproteins from different species

The erythrocyte membrane proteins and glycoproteins of man, rat, mouse, sheep and dog were analysed by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE), using a discontinuous buffer system. Considerable similarities between the species were observed in the pattern of protein bands seen when gels were stained with Coomassie Blue. Equivalents to human Bands 1, 2, 3, 4.2, 5 and 8 appeared to be present in the rat, mouse, sheep and dog, and Band 4.1 was identified as a closely spaced doublet in all species except the rat.When RBC membranes were stained with periodic acid-Schiff (PAS) after SDS-PAGE analysis, glycoproteins equivalent to human glycophorins were identified in all the species studied. However, in contrast to the overall similarity of the protein patterns, the number, relative staining intensity and apparent molecular masses of the PAS-stained bands differed between species.The silver stain was assessed in the detection of RBC membrane proteins in polyacrylamide gels, and found to be more sensitive than Coomassie Blue. The technique also stained many of the PAS-positive glycophorins as diffuse orange zones, which could be distinguished from the darker protein bands by their differential colouration.In view of the interspecies variation in the glycophorins after SDS-PAGE, it is suggested that, unlike the membrane proteins, their functions do not require a conserved structure.     

Antigens of infectious laryngotracheitis herpesvirus defined by monoclonal antibodies

Summary Monoclonal antibodies to glycoprotein and protein antigens of infectious laryngotracheitis virus (ILTV) were divided into five groups on the basis of their reactivity in immunofluorescence and Western blotting. Group I antibodies recognised a single band of 60 k and Group II antibodies recognised bands of 205, 160, 115, 90 and 85 k in Western blotting. In immunofluorescence both these groups of antibodies reacted with antigens located in the cytoplasm of fixed virus-infected cells and they also reacted with unfixed cells, suggesting that these antigens are on the surface of virus-infected cells. While Group I monoclonal antibodies did not react with extracts of tunicamycin-treated cells, some Group II antibodies recognised bands of decreased molecular weight compared to those present in untreated cells. The reactivity of the Group II antibodies with extracts of tunicamycin-treated cells suggested that they recognised at least three different epitopes which was confirmed by ELISA additivity assays. Monoclonal antibodies of Group III, Group IV and Group V recognised several low molecular weight proteins from 45 to 24 k. Immunofluorescence studies showed that these were nuclear and cytoplasmic antigens that were not present on the surface of virus-infected cells.     

T-cell specificity in murine autoimmune haemolytic anaemia induced by rat red blood cells

Autoimmune haemolytic anaemia (AIHA) can be induced in mice by repeated injections with rat red blood cells (RBC). Here we describe the identification of rat and murine RBC antigens recognized by T-cells from mice with this disease. Splenic T-cells from mice with AIHA proliferated in response to multiple murine RBC membrane components, each of which is recognized by rat RBC induced autoantibodies. Thus, there were responses to murine autoantigen fractions that correspond in apparent molecular mass with the anion channel Band 3, with spectrin from the membrane skeleton and with the high and low molecular mass glycophorins, and the equivalent fractions from rat RBC also stimulated proliferation by T-cells. It was confirmed that purified Band 3 from murine and rat RBC also elicited responses. In contrast with the results in AIHA, T-cells from healthy control mice failed to respond to the antigens from either species, with the exception of proliferation induced by murine spectrin in one experiment and weak responses elicited by rat Band 3. It is suggested that T-cells activated by multiple cross-reactions between rat and murine RBC proteins, and by epitope spreading, are necessary to drive autoantibody production in this model of AIHA.     

Control of T-cell-dependent antibody responses of mice to rat antigens by donor cell types

Administration of rat red blood cells (RBC) into mice induced a rat antigen-specific T-cell-dependent primary antibody response that was detected by a plaque assay using rat RBC as a target. This response was not induced by rat thymocytes or rat spleen cells that should share rat-specific antigens with rat RBC. We then demonstrated that rat spleen cells but not rat thymocytes, which were administered with rat RBC, partially inhibit the action of rat RBC for induction of the anti-rat response. This inhibition required live donor FcR+ cells, and seemed to be specific to rat antigens common to RBC and spleen cells. The findings supported the idea that the control by donor cell types, which was originally shown to work for T-cell-independent antibody response [3,5], should be effective for T-cell-dependent response beyond the species barrier.     

The inheritance of abnormal sialoglycoproteins found in a Gerbich negative individual

The Gerbich blood group antigens are probably expressed on one or more of the minor erythrocyte (beta, beta 1, or gamma) sialoglycoproteins which are lacking in some rare individuals having the Gerbich negative phenotype. A monoclonal antibody, CMRF-10, which recognises a trypsin-sensitive site on both the beta and beta 1 sialoglycoproteins, was tested for binding to erythrocytes from a Gerbich negative individual, OM. Erythrocytes from OM bound CMRF-10 in similar amounts to normal erythrocytes even though membranes from OM were shown by sodium dodecyl sulphate-polyacrylamide gel electrophoresis to lack both the beta and gamma sialoglycoproteins found in normal red blood cells. Instead, abnormal sialoglycoproteins which migrated as two bands with apparent molecular weights within the range 29,500-32,500 daltons were identified and purified using CMRF-10. Subsequent electrophoretic analysis of OM's two children failed to reveal any abnormal sialoglycoproteins. This suggests that in this instance the Gerbich negative phenotype may result from other mechanisms, possibly defective glycosylation, rather than a crossover involving the gene coding for the primary protein structure of the sialoglycoproteins.     

Experimental erythrocyte autoimmunity. IV. Differential susceptibility to irradiation of suppressor cells for anti-rat RBC antibodies and suppressor cells for mouse RBC autoantibodies

Mice injected with rat erythrocytes (RBC) produce RBC autoantibodies and antibodies against rat RBC. Transfer of spleen cells from autoantibody-producing mice to syngeneic recipients before the series of rat RBC injections causes a significant delay in autoantibody production although the response against rat RBC is elevated. Here it is shown that antibodies against rat RBC are markedly increased in recipients exposed to 350 rad of whole-body irradiation before transfer of spleen cells and the injections of rat RBC. In contrast, autoantibody production remained significantly suppressed. This shows that the anti-rat RBC response is regulated, at least in part, by cells in normal mice that are abrogated by 350 rad of whole-body irradiation.     

Virus-specific antibodies in sera from patients with genital herpes simplex virus infection.

Virus-specific antibodies against a number of herpes simplex virus type 2 antigens were determined by radioimmunoprecipitation assays in sequential serum samples obtained from 12 patients with initial genital herpes simplex virus infection. The progressive appearance of antibodies to virus-specific antigens was observed; antibodies against a 130,000-molecular-weight glycoprotein complex appeared first, followed by antibodies against the major nucleocapsid polypeptide and then antibodies against a number of other viral antigens, including a polypeptide with a molecular weight of 62,000. Patients who developed a wide variety of antibodies to viral polypeptides shortly after resolution of their initial episode seemed to experience more severe initial infections and more recurrences than did those who reacted poorly with these virus-specific antigens. This was most apparent with respect to antibodies to virus-specific polypeptides with molecular weights between 30,000 and 43,000. Antibody specificity did not change during the course of follow-up regardless of whether serum samples were taken shortly before, during, or after recurrent episodes. Glycoprotein-specific antibodies were quantitated with the purified 130,000-molecular-weight glycoprotein material. No significant fluctuations in these antibody titers were observed before or after recurrences of the disease.     

Isolation and partial characterization of the tegumental outer membrane of schistosomula of Schistosoma mansoni

Separation of the external membranes from freshly converted mechanical schistosomula of Schistosoma mansoni was achieved by osmotic shock under hypertonic conditions, followed by mechanical shearing and ultracentrifugation. Prior to treatment, the schistosomula were surface labeled by introduction of N-DNP-epsilon-aminocaproylphosphatidylethanolamine molecules into their lipid bilayer followed by anti-DNP antibodies and stained with either 125I-protein-A or ferritin labeled secondary anti-DNP antibodies. This label provided a membrane marker by which the purity of the preparation could be assessed at each stage. Fluorescence staining with FITC-conjugated secondary antibodies prior to treatment revealed that the homogeneously stained membrane of the intact schistosomula became swollen and ruptured after the osmotic shock. The isolated membrane pellet was intensely fluorescent. Electron microscopical examination revealed mostly vesicles, some of them with organized multilayer assembly. The vesicles were ferritin labeled, indicating that they originated from the outer surface membrane of the schistosomula. A 100 fold enrichment in the alkaline phosphatase activity and about 300 fold enrichment in acetylcholinesterase activity in the membrane preparations, as compared to the intact schistosomula, was found. The isolated tegument was analyzed by SDS-polyacrylamide gel electrophoresis. The pattern obtained showed three major bands, of molecular weights 69 000, 45 000 and 12 000 alongside with a large number of minor bands. Immunoprecipitation of the isolated 125I-labeled membrane antigens with antisera from chronically infected mice revealed these three major bands together with three other bands of molecular weight 38 000, 23 000 and 16 000.     

Isolation and Partial Characterization of Rat Lymphoid Cell Surface Histocompatibility Antigens and Immunoglobulins

Cell surface molecules of rat normal lymphoid cells were selectively labelled by lactoperoxidase catalysed iodination or by a galactose oxidase tritiated sodium borohydride technique, subsequently detergent solubilized, isolated by indirect immunoprecipitation and analysed on SDS-polyacrylamide gel electrophoresis. Four polypeptide chains were isolated by using the alloantiserum DA anti-Lewis. The molecular weights of the antigens were calculated as 41,000, 33,000, 27,000 and 12,000. Based on functional in vitro characteristics of the antiserum used and on the physiochemical properties as well as genetics of inheritance and tissue distribution, the polypeptide chains were identified as being subunits of Ag-B and Ia antigens. Two types of immunoglobulin heavy chains exhibiting the molecular weight 70,000 and 64,000 were isolated from unfractionated normal spleen cells by use of a polyvalent rabbit anti-rat immunoglobulin serum and tentatively identified as mu and delta chain. Using the same anti-immunoglobulin serum, no molecules could be precipitated from the lysated of Lewis thymocytes or peripheral T cells.     

The immune response to herpes simplex virus: comparison of the specificity and relative titers of serum antibodies directed against viral polypeptides following primary herpes simplex virus type 1 infections

Employing an immunoblotting technique, the polypeptide specificity and relative titers of anti-HSV IgG reactive with denaturation-resistant epitopes on HSV proteins were determined in patients experiencing primary HSV-1 infections at various anatomical sites. Early sera from previously seronegative patients with primary HSV-1 infections were found to have comparatively low levels of antibody directed against the major viral glycoprotein antigens (gB, gC, and gD) relative to titers present in sera of individuals with long-standing, latent orofacial HSV-1 infections. Patients with primary infections did however have high titers of antibody directed against a series of low molecular weight HSV polypeptide antigens. These antigens were found to be antigenically related to a structural component of virion nucleocapsids. At later times postinfection, titers of antibodies directed against other viral polypeptides including the major glycoproteins increased to levels more closely approximating those observed in latently infected individuals. These results indicate that the anti-HSV IgG detected by immunoblot analysis which appears earliest following primary infection is not directed against the known major infected cell or virion glycoprotein surface antigens but rather against an internal capsid protein of HSV.     

An immunoblotting procedure for screening glycophorins and band 3 protein in the same blots: Identification of glycophorin and band 3 variant forms

An immunoblotting procedure is described which makes it possible to screen multiple blood samples for the presence of glycophorin and band 3 variant forms with altered electrophoretic mobility. The procedure can be simplified by using whole red blood cell hemolysates instead of membranes for SDS-polyacrylamide gel electrophoresis. The use of hemolysates also has the advantage that antigens sensitive to proteolysis are not degraded in vitro. The same nitrocellulose blots were used for immunoenzymatic detection of glycophorins with a set of anti-glycophorin monoclonal antibodies, and for autoradiographic detection of band 3-derived bands with ¹²⁵I-labeled anti-band 3 monoclonal antibody. The screening of 157 Caucasian blood samples revealed the presence of a slower-migrating form of band 3 in seven cases and variant glycophorin in one case. The variant glycophorin exhibited the features of hybrid glycophorin of B-A type.     

Immune response after exposure to varicella zoster virus: characterization of virus-specific antibodies and their corresponding antigens.

Fourteen varicella zoster virus antigens were identified that induce antibodies during primary and recurrent infections. These antigens, which included the major nucleocapsid polypeptide (molecular weight, 155,000) and three glycoproteins (molecular weights, 130,000, 88,000, and 60,000, respectively) plus a number of minor antigens, were identified in radioimmunoprecipitation assays, using [35S]methionine-labeled extracts of cells infected with varicella zoster virus and sera from patients with primary and recurrent viral infections. No significant and reproducible differences were observed between early convalescent sera from cases with natural chicken pox and sera from cases with zoster in their ability react with viral antigens. Sera that were taken many years after episodes of chicken pox still retained their ability to react with the major viral antigens.     

Molecular cloning of Taenia taeniaeformis oncosphere antigen genes

Infection of mice with the cestode Taenia taeniaeformis exhibits several important features common to other cestode infections, including the ability to vaccinate with crude antigen mixtures. Partial purification of the protective oncosphere antigens has been reported with a cutout from deoxycholate (DOC) acrylamide gels; this cutout was called fraction II (FII), and comprises approximately 10% of total DOC-soluble oncosphere antigen. Western blots of DOC gels probed with anti-FII antisera revealed a series of 3-5 discrete bands within the FII region. Further fractionation of the FII antigens on DOC gels was impractical due to limitations in supply of oncospheres, so a cDNA library was constructed from 150 ng of oncosphere mRNA and screened with alpha-FII antisera. Two distinct clone families were identified, oncA and oncB. Antibodies affinity-purified on either of two representative members, oncA1 and oncB1, recognised all the FII bands. Individual FII bands excised from a DOC gel resolved into an overlapping series of molecules when re-run on SDS-PAGE, indicating that each FII band consisted of several polypeptides of differing molecular weight. Immunoprecipitates resolved on SDS-PAGE revealed that alpha-FII recognised 3 major oncosphere antigens, of 62, 34 and 25 kDa; antisera against oncB precipitated both the 34- and 25-kDa antigens, whereas alpha-oncA antisera precipitated the 62-kDa antigen. We conclude that oncA and oncB encode the major antigens in the FII complex. The 62-kDa antigen encoded by oncA1 was the only common antigen precipitated by anti-FII and two other antisera raised against different protective extracts, suggesting that it may be a protective component in all three. Southern blot results indicate that oncA and oncB are distinct genes present at low copy number in the genome. Evidence is also presented suggesting that some cestode mRNAs, including oncA, may use variant polyadenylation signals.     

Precursor-product relationship between nonglycosylated polypeptides of A and B particles of mouse mammary tumor virus.

Polypeptides and antigens of various preparations of intracytoplasmic A particles were analyzed in detail in comparison with those of B particles of mouse mammary tumor virus (MTV). SDS-polyacrylamide-gel electrophoresis (PAGE) revealed that B particles consisted of three major nonglycosylated polypeptides (B-p25, B-P15, and B-P7; numerals indicate calculated molecular weights in 10³ daltons) and six glycopeptides. All A-particle polypeptides were nonglycosylated. The particles purified by a conventional method contained seven major bands in the 70,000- to 37,000-molecular weight region, but their relative amounts varied from preparation to preparation. In most preparations, one other major band, A-p7 (an A-particle polypeptide with a molecular weight of 7000), was also observed. Thus, the polypeptide composition of A particles was quite different from that of B particles, having in common only one major band, p7, and three other bands of variable amounts, p43, p37, and p13. Those A particles that had been incubated at 37° for 20 hr showed a systematic change in PAGE pattern; major bands disappeared except for A-p43, A-p37, and A-p7, while a strong new band, A-p25, appeared. Consequently, incubated A particles were now similar to B particles in their PAGE pattern except for the absence of p15 in the-A particles. In spite of such a profound change in components, no ultrastructural alteration was observed in the A particles after incubation. Polypeptide conversion induced by incubation was completely inhibited by diisopropylfluorophosphonate (DFP). A particles purified in the presence of phenylmethanesulfonyl fluoride (PMSF) consisted of a single major polypeptide, A-p70. Incubation of these A particles resulted in generation of A-p15 in addition to A-p25 and A-p7 at the sacrifice of A-p70, although the rate of polypeptide conversion was much retarded. Antigenic analysis of individual polypeptides eluted from polyacrylamide gels shows that (i) B-p25, B-p15, and B-p7 carried distinct antigens; (ii) B-p25 and B-p7 were antigenically identical with A-p25 and A-p7, respectively; (iii) A-p70 carried all three of these different antigenicities of B particles; and (iv) other major polypeptides of A particles also carried these antigens in ways characteristic to each antigen. This indicates that three major internal components of B particles are generated from a common precursor, A-p70, through enzymatic cleavage and, hence, that A particles are the real pronucleocapsids of B particles. Present observations are discussed in connection with the precursor-product relationships proposed in other RNA tumor virus systems.     

Expression and regulation of erythrocyte auto-antibodies in mice following immunization with rat erythrocytes

Mice immunized with intact rat red blood cells (RBC) developed serum auto-antibodies (some of which were mouse specific) to the RBC membrane components spectrin and antigens of 100 and 81 kDa as shown by Western blotting and enzyme-linked immunosorbent assay as well as RBC surface-bound autoantibodies detected by the Coombs' test. In order to discover whether these autoantibodies were induced and controlled in similar or different ways, mice were challenged with a variety of rat and mouse RBC preparations. In addition, the ability of recipients given spleen cells from the above donors to generate autoantibody responses to intact rat RBC was measured. It was found that all the autoantibodies were induced in mice challenged with rat RBC ghosts but none following immunization with butanol-extracted rat RBC ghosts or intact mouse RBC. By contrast, mice injected with mouse RBC ghosts made autoantibodies to spectrin and to the 100-kDa band. Spleen cells from mice primed with intact rat RBC, rat RBC ghosts or butanol-extracted rat RBC ghosts curtailed Coombs' autoantibody production of recipient mice challenged with intact rat RBC. Serum from recipients of spleen cells primed with intact rat RBC or the butanol extract generally failed to react with rat or mouse spectrin or with the 81-kDa band, although antibody was detected to the rat 100-kDa band. Recipients of rat RBC ghost-primed spleen cells produced antibody to rat and mouse spectrin and to rat 100-kDa band but not to mouse 100-kDa or rat or mouse 81-kDa bands. Occasionally, suppression of antibody to the rat-specific 38-kDa band was observed in recipients of intact rat RBC-primed spleen cells. It is therefore suggested that regulation of cross-reactive and mouse-specific autoantibodies as well as rat-specific antibodies occurs in an independent, determinant-specific manner.     

Monoclonal antibodies that inhibit mitogenic activity of Mycoplasma pulmonis.

Previous studies have suggested a correlation between mitogenic, polyclonal activation of host lymphocytes and the respiratory tract inflammatory diseases induced by Mycoplasma pulmonis. This study describes the generation of monoclonal antibodies (MAbs) to M. pulmonis membrane antigens with different capacities to inhibit stimulation of cultured rat lymphocytes by mycoplasmal membranes and with variable effects on M. pulmonis growth. We show that the inhibitory effects exerted on mitogenesis by purified MAbs are inversely related to the effects of MAbs on M. pulmonis growth. Immunoblotting of electrophoretically separated membrane proteins, with both growth- and mitogenesis-inhibiting antibodies, revealed significant changes in the reactions obtained with both types of MAb following short exposure of membranes to heat. Growth-inhibiting MAbs strongly react with heat-labile antigenic complexes with molecular weights of 65,000 to 75,000. Inhibition of mitogenesis is mainly associated with recognition of membrane complexes of 84 to 113 kDa that exhibit disperse smears and variable heat sensitivities. Following brief heating of membranes, more distinct bands of 103, 90, and 84 kDa are obtained with MAbs that inhibit mitogenesis. Experiments with other mitogenic mycoplasma species and MAb 3.3.10.2, a potent inhibitor of mitogenesis reveal that whereas the antigenic epitope recognized by this antibody is present on unheated membranes from different mycoplasmas, with heated membranes the MAb yields reactions only with M. pulmonis and M. arthritidis. Our studies suggest that M. pulmonis mitogens are unique membrane complexes of variable molecular weights, highly susceptible to heat and less sensitive to reducing agents.     

Identification of tissue-specific antigens and concanavalin A receptors on rat epidermal cells using a radio-immunoprecipitation method.

Iodination with lactoperoxidase - 125I- - H2O2 was used to label surface components of rat epidermal cells. Lysis of the cells in non-idet P40 resulted in the solubilization of tissue-specific antigens and of concanavalin A receptors. These specificities were demonstrated using a radio-immunoprecipitation method. The tissue-specific antigens were recognized using absorbed rabbit anti-rat epidermal cell sera (Lloyd & Darnule 1974); they reacted with two low molecular weight components in the lysate (9,000 and 12,000 daltons). Concanavalin A reacted with three major components. Two had high molecular weights (75,000 and 95,000 daltons). The possibility that one of these components was radioiodinated lactooperoxidase, which would have reacted with concanavalin A, was disproved. Another component (which occasionally appeared as two peaks) was similar in size to the species detected by the tissue-specific antisera. Their non-identity was, however, demonstrated by the finding that the two specificities could be precipitated independently of each other.