Growth and reproduction complex in the rat. Genes linked to the major histocompatibility complex that affect development.

The linkage of the major histocompatibility complex (MHC) and the growth and reproduction complex (Grc) in the rat was studied in an F2 hybrid population generated from female BIL/1 (RT1l-Grc) and male YO (RT1u-Grc+) animals: 1.722 offspring were born, and 1,568 were weaned and studied. The body weights of the offspring segregated with the RT1 haplotype of the MHC, and the RT1l homozygotes were significantly smaller than their RT1l/u and RT1u/u littermates. The growth rate of the RT1l/l animals was approximately the same as that of the BIL/1 animals, and both were significantly less than the growth rates of the RT1l/u, RT1u/u, and YO (RT1u) animals. The testes of the RT1l animals showed an arrest of spermatogenesis at the early pachytene stage of the primary spermatocytes, and they were approximately 1/10 as heavy as the testes of the RT1l/u and RT1u/u animals. The ovaries in females of all three haplotypes had the same weight, but there was a decrease in the number of ova released per cycle in the RT1 l/l animals. The major loss of the RT1l homozygotes, which caused distortion of the phenotypic ratios among the offspring, did not occur in utero but in the early postnatal period before weaning. There were 7/1568 recombinants between the MHC, using the RT1.A antigen as the marker, and the Grc, using small body size (dw-3) as the marker, and 1/1568 recombinant between the loci influencing body size (dw-3) and fertility (ft) of the Grc. These data gave the following map distances (95% confidence levels): RT1.A to dw-3, 0.45 (0.25-0.96) centimorgans and dw-3 to ft, 0.07 (0.04-0.40) centimorgans. A female recombinant was used develop an inbred line carrying the RT1.Al-Grc+ chromosome.

Differential expression of MHC class I antigens on the placenta of the rat. A mechanism for the survival of the fetal allograft.

In some mating combinations in rats, there is a maternal antibody response to the maternal antigenic components of the placenta without any previous immunization of the mother. The highest response occurs in the WF (u) female mated to the DA (a) male, and it is against a unique MHC-encoded class I antigen, the Pa antigen, and not against the major allele-specific transplantation antigen of the DA strain, RT1.Aa. The development of mAbs to the Pa and Aa antigens allowed us to localize these antigens on the placenta and to explore the reason for the differential antibody response to them using immunohistochemical and biochemical techniques. Both antibodies reacted with the WF X DA placenta and stained the endovascular and interstitial trophoblast of the decidua, the basal trophoblast, Reichert's membrane, and the yolk sac epithelium, but they did not stain the labyrinthine trophoblast. Blocking studies showed that each antibody reacted with a separate molecule in the placenta. Anti-class II mAbs reactive with the a or u haplotype did not stain the WF X DA, DA X DA, or WF X WF placenta; hence, there are no class II antigens in the placenta. Electron microscopic studies of the semiallogeneic WF X DA placenta using the immunogold technique with both single- and double-labeling showed that only the Pa antigen was expressed on the surface of the basal trophoblast, but that both the Pa and Aa antigens were in the cytoplasm of these cells; neither antigen was found in the labyrinthine trophoblast. By contrast, the placenta from the syngeneic DA X DA mating expressed both the Pa and Aa antigens on the surface of the basal trophoblast as well as in the cytoplasm; neither antigen was found in the labyrinthine trophoblast. These observations were quantified morphometrically using electron photomicrographs of single-labeled tissues. Both the Pa and Aa antigens isolated from the plasma membrane of lymphocytes have heavy chains of 46 kD, but those antigens isolated from the plasma membrane of basal trophoblast cells have heavy chains of 43 kD. Based on densitometric measurements of autoradiographs, the Pa/Aa ratio in the basal trophoblast membrane is 23.5, whereas it is 0.46 in lymphocyte membranes. These studies show that there is differential regulation of the expression of class I antigens on basal trophoblast cells in semiallogeneic pregnancies, but not in syngeneic pregnancies, such that the major allele-specific transplantation antigen is scarcely expressed on the surface of the basal trophoblast.(ABSTRACT TRUNCATED AT 400 WORDS)

In-vivo time-dependent articular cartilage contact behavior of the tibiofemoral joint.

OBJECTIVE: The purpose of this study was to investigate the in-vivo time-dependent contact behavior of tibiofemoral cartilage of human subjects during the first 300 s after applying a constant full body weight loading and determine whether there are differences in cartilage contact responses between the medial and lateral compartments. DESIGN: Six healthy knees were investigated in this study. Each knee joint was subjected to full body weight loading and the in-vivo positions of the knee were captured by two orthogonal fluoroscopes during the first 300 s after applying the load. Three-dimensional models of the knee were created from MR images and used to reproduce the in-vivo knee positions recorded by the fluoroscopes. The time-dependent contact behavior of the cartilage was represented using the peak cartilage contact deformation and the cartilage contact area as functions of time under the constant full body weight. RESULTS: Both medial and lateral compartments showed a rapid increase in contact deformation and contact area during the first 20s of loading. After 50s of loading, the peak contact deformation values were 10.5+/-0.8% (medial) and 12.6+/-3.4% (lateral), and the contact areas were 223.9+/-14.8 mm(2) (medial) and 123.0+/-22.8 mm(2) (lateral). Thereafter, the peak cartilage contact deformation and contact area remained relatively constant. The respective changing rates of cartilage contact deformation were 1.4+/-0.9%/s (medial) and 3.1+/-2.5%/s (lateral); and of contact areas were 40.6+/-20.8 mm(2)/s (medial) and 24.0+/-11.4 mm(2)/s (lateral), at the first second of loading. Beyond 50 s, both changing rates approached zero. CONCLUSIONS: The peak cartilage contact deformation increased rapidly within the first 20s of loading and remained relatively constant after approximately 50 s of loading. The time-dependent response of cartilage contact behavior under constant full body weight loading was significantly different in the medial and lateral tibiofemoral compartments, with greater peak cartilage contact deformation on the lateral side and greater contact area on the medial side. These data can provide insight into normal in-vivo cartilage function and provide guidelines for the improvement of ex-vivo cartilage experiments and the validation of computational models that simulate human knee joint contact.

Physical chemical studies on the specific interaction of an acriflavine-phosphotungstic Acid complex with double-stranded nucleic acids.

The detailed definition of the structure of DNA in chromosomes and in interphase chromatin is important for correlating the structure of the genetic material with various states of physiological activity. A general approach to developing specific reagents for a variety of such studies in solution and in tissues is to combine a chemically specific organic cation with the electron-opaque phosphotungstic acid (PTA) molecule. The reagent described in this paper was made from the interaction of acriflavine and phosphotungstic acid. The acriflavine-PTA complex (a) displays some unique absorption and fluorescence properties, (b) binds specifically to DNA and RNA by intercalation of the acriflavine moiety, and (c) is electron opaque. In addition, it binds to double-stranded synthetic polynucleotides, but not to a variety of proteins, nucleoproteins, or polysaccharides.

Maternal-fetal interaction and immunological memory.

Female rats of the poorly responding, inbred F344 strain were immunized with poly(Glu(52)Lys(33)Tyr(15)) aggregated with methylated bovine serum albumin, and then they were mated. The first and second litters in the F(1) generation and in the F(2) generation showed an enhanced immune response. When poly-lysine was used as the aggregating agent, enhancement occurred in only the first litter of the F(1) generation and in the F(2) generation. In both cases, antigen was transmitted from the immunized female to her offspring, where it localized in the bone marrow and, in a few cases, in the thymus and spleen also. The transplacental passage of antigen is probably the basis for the enhanced antibody response, which is a manifestation of immunological memory.

The rat as an experimental animal.

The development and characterization of many inbred, congenic, and recombinant strains of rats in recent years has led to the detailed genetic description of this species, especially in regard to its major histocompatibility complex. This information has contributed substantially to the study of comparative genetics and has greatly enhanced the utility of the rat in a variety of areas of biomedical research. This article focuses on the use of the rat in immunogenetics, transplantation, cancer-risk assessment, cardiovascular diseases, and behavior.

In vivo cartilage contact deformation in the healthy human tibiofemoral joint.

OBJECTIVES: In vivo cartilage contact deformation is instrumental for understanding human joint function and degeneration. This study measured the total deformation of contacting articular cartilage in the human tibiofemoral joint during in vivo weight-bearing flexion. METHODS: Eleven healthy knees were magnetic resonance (MR) scanned and imaged with a dual fluoroscopic system while the subject performed a weight-bearing single-leg lunge. The tibia, femur and associated articulating cartilage were constructed from the MR images and combined with the dual fluoroscopic images to determine in vivo cartilage contact deformation from full extension to 120 degrees of flexion. RESULTS: In both compartments, minimum peak compartmental contact deformation occurred at 30 degrees of flexion (24 +/- 6% medial, 17 +/- 7% lateral) and maximum peak compartmental deformation occurred at 120 degrees of flexion (30 +/- 13% medial, 30 +/- 10% lateral) during the weight-bearing flexion from full extension to 120 degrees. Average medial contact areas and peak contact deformations were significantly greater than lateral compartment values (P < 0.05). In addition, cartilage thickness in regions of contact was on average 1.4- and 1.1-times thicker than the average thickness of the tibial and femoral cartilage surfaces, respectively (P < 0.05). CONCLUSIONS: These data may provide base-line knowledge for investigating the effects of various knee injuries on joint contact biomechanics and the aetiology of cartilage degeneration.

Transplacental immunization of the human fetus to tetanus by immunization of the mother.

Experimental studies in rats showed that immunization of the pregnant female led to the transplacental immunization of her fetuses. The possibility that this also occurred in humans was explored by immunizing 42 pregnant women with tetanus toxoid (2.5 or 5 Lf) in the fifth and eighth months of pregnancy and comparing the immune responses of their offspring with the responses of the offspring of 25 unimmunized mothers. Only the offspring of the immunized mothers were sensitized to tetanus. IgM antitetanus antibodies were in their blood before immunization with diphtheria, pertussis, tetanus vaccine (DPT), they had a more rapid (P less than 0.01) response to DPT immunization, and they were still highly sensitized (P less than 0.01) to tetanus 13 mo after birth. In addition, pregnancy had no immunosuppressive effect (P less than 0.05) on the responses of the mothers to tetanus toxoid. Thus, transplacental immunization occurs in humans; it enhances the response of the offspring to subsequent immunization, and it could be used to circumvent the necessity for immunization in early neonatal life.

Effects of oral versus topical administration of cyclosporine on phorbol ester promotion of murine epidermal carcinogenesis.

In murine epidermal carcinogenesis, topical applications of cyclosporine (CsA), an immunosuppressant, have been reported to suppress 12-O-tetradecanoylphorbol-13-acetate (TPA) promotion. In the present study, we compared the effects of p.o. versus topical CsA on TPA promotion of mouse skin tumors and on TPA-induced epidermal hyperplasia. In the first series, groups of male Swiss Webster mice were initiated with 7,12-dimethylbenz(a)anthracene (200 nmol), and 3 days later they were placed on a basal diet or a diet containing 0.015% CsA. Then both groups of mice were promoted twice weekly with TPA (10 nmol) for 22 wk and observed for an additional 13 wk without TPA. No significant difference was observed in the incidence of skin papillomas between the 2 groups. By contrast, the incidences of squamous cell carcinomas in the mice maintained on CsA and basal diet were 67% and 28%, respectively. In the second series, the mice initiated with 200 nmol of 7,12-dimethylbenz(a)anthracene were treated twice weekly with 10 or 5 nmol of TPA for 24 wk. Ten to 15 min prior to each TPA application, one group received topical CsA in acetone (1 mg/mouse), and the other acetone. There was a significant inhibition of TPA promotion in the mice given topical CsA. Topical and p.o. CsA had no significant effect on epidermal hyperplasia induced by 4- to 8-wk treatment of TPA. The mice given topical CsA showed less inflammatory cell infiltrates in the dermis than the mice without CsA. The results indicate that the effect of CsA on TPA promotion of skin tumors depends on its routes of administration, and the p.o. administration enhances the progression of papillomas to squamous cell carcinomas.

Immunogenetic control of brain tumor growth in rats.

The susceptibility to intracerebral and s.c. growth of a transplantable gliosarcoma in genetically inbred rats correlated with histocompatibility type. The genetic control of tumor growth was tested in a cross between a tumor-susceptible strain (F344, Ag-B1) and a tumor-resistant strain (YO, Ag-B2). Susceptibility was transmitted as a dominant trait, and at least two genes or gene complexes were involved: one was linked to the major histocompatibility complex and one segregated independently of it. The genetic mechanisms did not appear to be affected significantly by the site (environment) in which the tumor grew. Antibodies to Ag-B1 histocompatibility antigens, which were those of the strain in which the tumor originated (F344), and to tumor-associated antigens were generally present in animals in which the tumor had regressed. Only tumor-specific antibodies appeared in the sera of Ag-B1 animals that had the tumor. A cytotoxic lymphokine was present in the sera of tumor-bearing animals, but its level did not correlate with tumor growth or regression.

Cell lines from grc congenic strains of rats having different susceptibilities to chemical carcinogens.

The growth and reproduction complex (grc-) strains of rats have a 70-kilobase deletion in the major histocompatibility complex (MHC)-linked grc-G/C region that is associated with embryonic death, developmental defects, and an increased susceptibility to chemical carcinogens. To study further the effects associated with the deletion, fibroblastic cell lines from grc-, grc+, and grc+/- rat embryos were developed: BIL-derived cell lines are congenic for the MHC and grc, whereas R16-derived cell lines are congenic for the grc alone. In early passages, all cell lines expressed the MHC class I antigen RT1.A, had a diploid chromosome number, and did not display anchorage-independent growth or in vivo tumorigenicity. The grc- cells [median population doubling time (PDT), 47 h] grew more slowly than the grc+ (PDT, 30.5 h) and grc+/- (PDT, 33 h) cells. All cells underwent crisis, but the crisis stage began earlier and lasted longer in the grc- cells. The established grc- cell lines (PDT, 32.5 h) grew faster than the grc+ (PDT, 48.5 h) and grc+/- (PDT, 54 h) cell lines. Two of the three BIL-derived grc- lines that survived crisis became anchorage independent in tissue culture and tumorigenic in histocompatible F1 rats (highly malignant fibrosarcomas) at passages 33 and 48, respectively; by contrast, none of the R16-derived grc- cell lines transformed. None of 8 grc+ or 8 grc+/- cell lines that survived crisis displayed anchorage-independent growth or tumorigenicity under the same conditions up to passage 50. All of the established cell lines, including the two tumorigenic ones, expressed MHC class I antigens. Southern and Northern blot analyses of BIL-derived cell lines before and after crisis showed that they all constitutively expressed H-ras and Rb and that no cell line showed rearrangement, amplification, or overexpression of c-myc, H-ras, Rb, and p53 either before or after crisis. These observations indicate that: (a) the homozygous grc- deletion is necessary but not sufficient for in vitro transformation; (b) another genetic factor(s) required for transformation is linked to, or possibly in, the MHC; and (c) passage through crisis, spontaneous transformation, or carcinogen treatment does not alter the cellular expression of MHC class I antigens or of several oncogenes and tumor suppressor genes.

Genetic control of susceptibility to diethylnitrosamine carcinogenesis in inbred ACP (grc+) and R16 (grc) rats.

The R16 strain, which carries the major histocompatibility complex-linked growth and reproduction complex (grc), and its normal counterpart, the ACP strain, were initiated at 8 wk of age with a single i.p. dose of diethylnitrosamine (DEN), and 2 wk later they were fed either a choline-deficient (CD) or a choline-supplemented (CS) diet. The rats were sacrificed 2, 4, 6, 10, and 12 mo later; complete autopsies were performed, and all of the tissues were examined histologically. Sections of the liver were also examined histochemically for gamma-glutamyl transpeptidase activity. Shortly after the administration of DEN, the R16 strain showed a significant increase in the number and size of gamma-glutamyl transpeptidase-positive foci and more severe histological changes (disruption of the lobular architecture, bile duct and oval cell proliferation, cellular atypia, and accumulation of fat) compared with the ACP strain. These changes occurred in animals fed either CD or CS diet, but they were much more extensive and severe in the animals on the CD diet. They did not occur in rats of either strain fed the diets alone. The first hepatocellular carcinoma appeared in the R16 rats on the CD diet at 4 mo after administration of the DEN and on the CS diet, at 10 mo. The only hepatocellular carcinoma that occurred in the ACP rats did so at 12 mo in one animal on the CD diet. Combining the data at 10 and 12 mo for the rats on the CD diet, 50% (20 of 40) of the R16 rats had hepatocellular carcinomas, whereas only 3% (one of 30) of ACP rats did. The R16 strain (22%, 9 of 40), but not the ACP strain (0 of 30), also had a variety of other malignancies: squamous cell carcinomas (8%); renal cell carcinomas (8%); lymphomas (5%); and pheochromocytoma (3%). A similar pattern of malignancies also occurred in the R16 rats on the CS diet, and there were no malignancies in the ACP rats. These observations indicate that the grc confers unusual susceptibility to the induction of cancer by the chemical carcinogen DEN and that this genetic susceptibility to cancer of the R16 strain extends beyond the primary target organ of the carcinogen used.

Lymphocyte plasma membranes. VI. Plasma membrane glycoproteins of thymic and splenic lymphocytes from inbred rats.

Plasma membranes of splenic and thymic lymphocytes from ACI rats were analyzed for their protein and glycoprotein components by surface radioiodination with 125I and SDS-polyacrylamide gel electrophoresis. The glycoproteins were extracted with lithium diiodosalicylate, characterized and assayed with antisera to thymic antigen. Plasma membranes of both cell types showed more than 25 proteins of which 10--15 were glycoproteins. Both cells showed five major glycoproteins but their apparent molecular weights or intensities differed. Surface radioiodination showed a 120 000 daltons component, common to both cell types, and a 27 000 daltons thymus-specific component as the most exposed surface glycoproteins. Lithium diiodosalicylate extracts of the plasma membranes contained almost all of the glycoprotein components and comprised 5-6 percent of the total membrane protein and 40-50 percent of the total membrane carbohydrate, with sialic acid content in thymus twice that of the spleen cells. About 1 percent of the total plasma membrane protein and 7 percent of the total isolated glycoproteins from thymocytes were reactive with rabbit anti-rat thymocyte antiserum and the immune precipitates showed two components with apparent molecular weights of 72 000 and 27 000.

Lymphocyte plasma membranes. III. Composition of lymphocyte plasma membranes from normal and immunized rats.

Isolated plasma membranes of thymic and splenic lymphocytes from unimmunized and immunized rats of the inbred ACI and F344 strains were analyzed for chemical and enzymatic composition, for membrane protein patterns by polyacrylamide gel electrophoresis and for membrane-associated immunoglobulins. After immunization, the thymic and splenic lymphocyte membranes from F344 rat contained less carbohydrate and higher phospholipid contents than control animals. In both ACI and F344 inbred rat strains the membrane phospholipid to cholesterol weight ratio increased significantly after immunization. The electrophoretic patterns of solubilized membrane proteins and of iodinated external membrane proteins were similar in unimmunized and immunized animals. When thymic and splenic lymphocytes of normal or immunized animals were surface radioidinated, solubilized in Triton X-100, NP-40 or 10 M urea in 1.5 M acetic acid and analyzed by immunoprecipitation, labeled IgM immunoglobulin was recovered from thymic lymphocytes but both labeled IgG and IgM were recovered from splenic lymphocytes. However, when unlabeled isolated plasma membranes were solubilized in 1 percent Triton X-100 and analyzed by immunodiffusion in agarose gels both IgG and IgM were identified in thymic and splenic cells.

Genic interaction causing embryonic mortality in the rat: epistasis between the Tal and grc genes.

The autosomal dominant mutant gene, tail anomaly lethal (Tal), of the rat is lethal when homozygous but affects tail morphology (kinks and reduced length) and body weight when heterozygous. There is no apparent sex effect on the expression of Tal. It is incompletely penetrant; has variable expressivity, which is influenced partly by its genetic background; and is not linked to the major histocompatibility complex (MHC). The heterozygous Tal gene and the homozygous grc genes, which are linked to the MHC and affect body size and fertility, interact to cause intrauterine death at a time between implantation (five to seven days post-fertilization) and 15 days of gestation. This interaction shifts the time of death from the immediate postnatal period when the homozygous grc genes act to the time during gestation when the homozygous Tal gene would cause death. This description of lethal epistatic interaction in the rat appears to be the first report of this phenomenon in mammals.

Genetic analysis of liver neuraminidase isozymes in Rattus norvegicus: independent control of NEU-1 and NEU-2 phenotypes.

Two recently identified isozymes of neuraminidase in rat liver were examined for transmission patterns and linkage relationships, and for variation among inbred strains. The isozymes, designated neuraminidase-1 (NEU-1) and neuraminidase-2 (NEU-2), exhibited no electrophoretic mobility variants among the 22 inbred strains examined, but did possess striking interstrain variation in activity phenotypes on electrophoretic gels. The results of a backcross analysis involving the KGH and ACP strains revealed that NEU-1 and NEU-2 phenotypes are independently controlled, each by a single autosomal locus with additively acting alleles. The two loci are unlinked to one another, but the gene controlling NEU-1 is tightly linked to RT1, the rat major histocompatibility complex. This gene is almost certainly identical to Neu-1, a gene identified previously through its effect on "total" activity levels of liver neuraminidase as determined by fluorometric assay of tissue homogenates. NEU-2 and the gene controlling its phenotype were not detected by the fluorometric technique. We designate the genes controlling the NEU-1 and NEU-2 phenotypes as Neu-1 and Neu-2, respectively. Data from this and other studies place Neu-1 between Glo-1 and dw-3. The location of Neu-2 is unknown.

The Ah phenotype. Survey of forty-eight rat strains and twenty inbred mouse strains.

Forty-four inbred and four randombred rat strains and 20 inbred mouse strains were examined for their Ah phenotype by determining the induction of liver microsomal aryl hydrocarbon (benzo[a]pyrene) hydroxylase activity (EC 1.14.14.1) by intraperitoneal treatment with either beta-naphthoflavone or 3-methylcholanthrene. All 48 rat strains were found to be Ah-responsive. The maximally induced hydroxylase specific activities of the ALB/Pit, MNR/Pit, MR/Pit, SHR/Pit, and Sprague-Dawley strains were of the same order of magnitude as the basal hydroxylase specific activities of the ACI/Pit, F344/Pit, OKA/Pit, and MNR/N strains. Six of the 20 mouse strains were Ah-nonresponsive (i.e. lacking the normal induction response and presumably lacking detectable amounts of the Ah receptor). The basal hydroxylase specific activities of the BDL/N, NFS/N, STAR/N, and ST/JN mouse strains were more than twice as high as the maximally induced hydroxylase specific activity of the CBA/HT strain.--To date, 24 Ah-nonresponsive mouse strains have been identified, out of a total of 68 known to have been characterized. The reasons for not finding a single Ah-nonresponsive inbred rat strain--as compared with about one Ah-nonresponsive inbred mouse strain found for every three examined--remain unknown.

Immunity and pregnancy.

The existence of the maternal immune response to various paternally derived antigens on the fetus and placenta is apparently paradoxical, since the immune response is generally associated with host defense. In this context, the immune response to the fetal and placental antigens may have either physiological function or be advantitious. In either event, it appears to be closely associated with the existence of the polymorphisms of the cell surface antigens, particularly those controlled by the genes in the major histocompatibility complex. The major thrust of this review will be to examine the nature of the humoral and cellular immune response to the fetus and placenta and the genetic factors influencing it. A second portion of the review will address the genetic factors influencing development, including those involved in spontaneous abortion and in the genetic control of developmental abnormalities.

Cellular events associated with peripherally induced rejection of mature neural xenografts placed into neonatal rat brains.

Various circumstances have brought about a dispute concerning the immunologically priviledged status of the central nervous system (CNS). Using a transplantation paradigm, we have examined the cellular events associated with an experimentally induced focal assault on the CNS by the immune system. Chunks of embryonic mouse cortex were transplanted into neonatal rat brains and allowed to survive for 4 weeks. The adult rats then received a skin graft of donor origin to induce rejection of the transplanted tissue. Animals were sacrificed at various time points and examined histologically and immunocytochemically. Under these circumstances, the transplant is rejected via a first-set rejection response, and astrocytes of donor origin appear to be the primary target of the host immune system. Expression of class I and class II major histocompatibility antigens is noted to correlate with lymphocytic invasion of the transplant.

Radioimmunoassay of IgM and IgG antitetanus toxoid antibody.

A radioimmunoassay was developed to quantitate antitetanus toxoid antibody in whole plasma which can detect 0.75 ng IgG antibody (0.75 micrograms/ml plasma) and 1.60 ng IgM antibody (0.40 micrograms/ml plasma). The IgG antibody was measured by direct binding to a tetanus toxoid-Sepharose immunoadsorbent. The IgM antibody was measured by inhibition of binding by soluble tetanus toxoid because of the relatively high and erratic nonspecific reaction between IgM and the immunoadsorbent. The immunoglobulin standards were [131I]IgG or [131I]IgM coupled to Sepharose, respectively, and the amount of antibody activity in the 125I-labeled antiglobulin reagents could be calculated from the amount bound to the immunoadsorbent and the specific activity of the appropriate immunoglobulin standard. The assay is sensitive, reproducible and suitable for use with large numbers of samples: it should find wide applicability in both clinical and experimental settings.