The structural basis for binding of complement by immunoglobulin M.

An insight into the structural features of human IgM that are responsible for its capacity to bind the first component of complement (C) has been obtained by examining the ability of IgM subfragments to bind active C1 (C1). The smallest two fragments found to bind C1 were the major CNBr fragment of the Fc portion of IgM and the C(H)4 fragment of the carboxy-terminal domain. The smallest fragment which fixes C1 has a disaggregated mol wt of 6,800, consists of 60 residues, and contains no carbohydrate. Structural considerations and sequence overlaps suggest that the amino-terminal side of the C(H)4 domain (24 amino acid residues) might be responsible for fixing C1.

Differential expression of class I major histocompatibility complex determinants by lymphoblastic leukemia-lymphoma cell lines.

Two T-cell lines (XR11-4T and XR11-5T), established from radiation-induced, murine lymphoblastic lymphomas, were examined for the expression of class I major histocompatibility complex antigen and tumor induction. These cell lines expressed class I private determinants, H-2.9 and H-2.26, but not the monomorphic determinant defined by monoclonal antibody M1/42. Both cell lines produced tumors in syngeneic and allogeneic hosts. The monomorphic determinant could be demonstrated on both cell lines following growth in allogeneic (BALB/c mice) but not in syngeneic (RFM mice) hosts. The re-expressed determinant present on cells following growth in allogeneic mice was not of host origin. Thus, tumorigenic x irradiation may differentially affect the expression of class I major histocompatibility complex determinants.

Expression of 44-kilodalton oncofetal antigen as a premalignancy marker in X irradiation-induced murine T-cell lymphoma.

BACKGROUND: Oncofetal antigens (OFAs) are found on the surface of murine and human midgestation fetal cells, in human and rodent tumor tissues, and on human and rodent tumor and embryonic cell lines but not in normal neonatal or adult human and rodent tissue. PURPOSE: The usefulness of OFA as an early indicator of lymphoma development was evaluated. METHODS: With the use of monoclonal antibody directed against a 44-kd glycoprotein, cells from the thymus and spleen of RFM/UnCr mice receiving whole-body, split-dose x irradiation (1.75 Gy once a week for 4 weeks) or cells from these organs from control (nonirradiated) mice were analyzed for the presence of OFA in the flow cytometer and in limited intrathymic transplant. RESULTS: OFA was detected on thymocytes from 75% of irradiated mice by 2 months after treatment, reflecting eventual lymphoma development in the irradiated controls by flow cytometry and in intrathymic transplant. In general, the number of thymuses expressing OFA and the percentage of OFA+ cells increased with time after irradiation. By 4 months, OFA+ splenocytes were present, but only in mice possessing OFA+ thymocytes. Serially tested, irradiated RFM mice that never expressed OFA in the thymus reflected the percentage of irradiated RFM/UnCr mice that never developed lymphomas. This observation was also made in irradiated C57BL/6N mice, which attests to the tumor specificity of OFA expression. Spleen immunoglobulin-positive cells were decreased, while CD4+ and CD8+ cells were greatly increased. Indirect evidence of CD4/CD8 expression on OFA+ splenocytes suggests that the newly forming lymphomas were of immature T-cell origin. Major histocompatibility antigen expression did not vary significantly. Histopathologic examination revealed radiation-induced lymphomas in OFA-positive tissues characterized by a monomorphic population of large blastic immature lymphoid cells. CONCLUSION: The early expression of OFA in radiation-induced oncogenesis was established. IMPLICATIONS: OFA expression significantly preceded clear histologic evidence of malignant T cells or clinical lymphoma in irradiated RFM/UnCr mice that went on to develop T-cell lymphomas.

Acetazolamide in the treatment of abnormal oculovestibular response.

We treated seven patients with incapacitating vertigo elicited by walking down a grocery store aisle or driving a car. Results of neurologic, neuro-ophthalmic, and neuroradiologic examinations were normal. Episodic vertigo secondary to an abnormal oculovestibular response was diagnosed. Each patient was given a trial of 250 to 500 mg of acetazolamide daily. Symptoms resolved completely in four patients, two patients had near resolution of symptoms, and one patient had no relief. Carbonic anhydrase activity has been demonstrated in the inner ear, and acetazolamide has been shown to affect the ion balance of the inner ear fluids.

Confocal laser scanning microscopy and three-dimensional reconstruction of cell clusters in serous fluids.

Thick cell clusters are a common finding in reactive and malignant effusions. In order to arrive at a diagnosis, clusters are evaluated for certain cytomorphologic features including size, shape, smooth vs. scalloped borders, and three-dimensional (3-D) configuration. By conventional microscopy, the image of these clusters is often blurred due to limitations in resolution. Consequently, the exact internal structure and cellular arrangement within these clusters cannot be adequately determined. Utilizing confocal laser scanning microscopy (CLSM), we examined serous fluids from a variety of conditions. Cases included mesothelioma, adenocarcinoma, and papillary adenocarcinoma. Smears were stained with 0.01% ethidium bromide and 1% eosin Y, followed by analysis with an ACAS 570 image analyzer (Meridian Instruments, Inc. Okemos, MI). Serial confocal fluorescence images were acquired, which allowed 3-D reconstruction of the clusters. Mesothelioma clusters (excluding those with obvious central collagen cores by light microscopy) appeared to be formed of the following configurations: 1) randomly coiled cords of cells, 2) small papillae encompassing central cores, and 3) tissue fragments with pseudoacinar formation. In contrast, adenocarcinomas had a more orderly pattern, with tightly cohesive cells and true acinar formation.

Tumorigenic sublethal whole-body X-irradiation of RFM mice enhances cell-mediated cytotoxicity while transiently depressing T- and B-lymphocytes.

The immunocyte composition of spleens and peritoneal exudates (PEC) from RFM mice was examined following tumorigenic doses of whole-body, sublethal X-irradiation. T-cells, B-cells and macrophages were quantitated using mAb and flow cytometry. The cell mediated cytotoxicity (CMC) potential of PEC following immunization with allogeneic tumor cells was also assayed. Although the percentages of T- and B-cells were depressed in irradiated mice, the CMC activity of PEC from these same mice was increased. Thus irradiation resulted in an increased incidence of tumors coincident with an increased CMC potential against tumor targets.

Reassembly of immunoglobulin M heavy and light chains in vitro.

Reduced and alkylated monoclonal IgM was fractionated into mu and light (L) chains by gel chromatography in 1N acetic acid. Equimolar mixtures of the chains formed a noncovalently bonded structure in 0.01M sodium acetate buffer, pH 4.1, that had the properties of a half subunit. The latter reassociated into a subunit-like structure after transfer into 0.08M sodium phosphate buffer, pH 7.5. The similarity of the reconstituted IgM subunit (IgMs) to that of the native molecule was established by its physicochemical and immunochemical properties. Comparable products were obtained on reassembly of the alkylated mu and L chains from several other monoclonal IgM. The presence of active binding sites for IgG on subunits reconstituted from the chains of proteins with anti-IgG activity further indicated correct assembly of the mu and L chains. High yields of subunit-like products were also obtained by assembly of mu chains from one protein and L chains from another. Evidence was obtained that L chains of appropriate specificity can substitute for the homologous chain in the formation of the active site. Heterogeneous mixtures of high molecular weight products were generated from mu and L chains that were not alkylated. Reduction and alkylation demonstrated that the products represented polymers of reconstituted IgMs. Significant levels of anti-IgG activity were detected in the polymeric IgM generated from the chains of active proteins by precipitation with aggregated IgG.

Studies on the cytophilic properties of human beta2-microglobulin. II. The role of histocompatibility antigens.

The mechanism by which exogenously added beta2m binds to lymphoid cells has been explored. In the mouse it has been shown that beta2m remains associated with plasma membrane macromolecules following solubilization with NP-40 and that approximately 25-30% of the binding could be accounted for by binding to H-2 antigens. No binding to mouse immunoglobulin or Ia antigens could be detected. The sites for binding of the remainder of the cell-bound beta2m were not determined. Whereas normal human lymphocytes showed little or no capacity to bind exogenously added beta2m, it was found that phytohaemagglutinin (PHA)-stimulated cells could bind beta2m. This binding occurred optimally 2 days after PHA stimulation. Approximately half of the binding could be accounted for by binding to HLA antigens. The possible significance of these findings with respect to cellular interactions involving major histocompatibility complex gene products in the immune response is discussed.

Evidence for the absence of noncovalent bonds in the Fcmu region of IgM.

IgM isolated from the sera of five patients with Waldenström's macroglobulinemia was subjected to tryptic digestion at 60 degrees C. The Fc5mu fragments recovered from the digests were reduced by 0.05 M cysteine and alkylated by iodoacetamide, producing large quantities of an Fcmu fragment having a sedimentation velocity (see article) of 2.9S and a molecular weight of 33,500 by sedimentation equilibrium in neutral buffer. Further studies on the Fcmu fragment from one of the proteins demonstrated that it was not dissociated into smaller fragments by 5 M guanidine-HC1, even after reduction with 0.1 M 2-mercaptoethanol in 5 M guanidine at pH 7.5. The number of sulfhydryl groups released by the latter treatment indicated the presence of two intrachain disulfide bonds. These observations provide evidence that this portion of the mu-chain demonstrates minimal noncovalent interactions. Tryptic digestion of the Fcmu fragment at 37 degrees C resulted in the production of several lower molecular weight fractions. The three major fractions demonstrated apparent molecular weights of 21,000, 13,800 and 6800 by sedimentation equilibrium in 5 M guanidine-HC1. The latter fraction (fraction C) had no detectable carbohydrate and consisted of two disulfide-bonded peptides having molecular weights of approximately 3800 and 2200. Studies on the amino acid composition and amino-terminal sequences indicated that fraction C was derived from the Cmu4 homology region and consisted of residues 468 through 546 of the mu-chain with the tryptic peptides encompassing residues 492 through 514 missing.

Persistent expression of Ia-antigen on a subpopulation of murine resident peritoneal macrophages.

The stability of Ia-antigen expression on murine resident peritoneal macrophages was assessed during the course of in vitro culture. Contrary to published findings with radioimmunoassays and immunofluorescence assays, the cultured cells bore Ia-antigen, as shown by their rosetting with sheep erythrocytes coupled with anti-Ia.2 monoclonal antibody. In support of this finding, cultured cells presented the copolymer of glutamine, alanine, and tyrosine (GAT) to GAT-primed T lymphocytes in an Ia-dependent manner. Thus, functional Ia antigen is present on cultured macrophages. Disappearance of the antigen after fixation of macrophages with either glutaraldehyde or paraformaldehyde, a routine procedure in the radioimmunoassays and immunofluorescence assays, explains its presumed absence on cultured cells.

Increased oxygen tensions influence subset composition of the cellular immune system in aged mice.

In acute and chronic experiments, each of eight groups of aged mice were assigned separately to different pressures of oxygen to which it was to be exposed. Lymphocytes from spleen, thymus, and peripheral blood were analyzed following oxygen exposure. Subset populations changed depending on the oxygen tension. Variable changes were observed in total numbers of lymphocytes, lymphocyte subsets, B cells, and macrophages depending on the organ studied and the oxygen pressure to which the mice were exposed. There were differences between acute and chronic exposure suggestive of adaptation to environmental stressors. The suggestion is made that the immune system has a reserve capacity that can be influenced by oxygen and, thereby, theoretically capable of being pharmacologically manipulated to assist patients with altered immune systems to promote defense mechanisms or, under certain circumstances, reduce autoimmunity. It is hypothesized that an underlying hypoxia may be involved in the age-associated decline in the immune system.

Increased oxygen tensions modulate the cellular composition of the adaptive immune system in BALB/c mice.

In acute and chronic experiments, each of eight groups of young mice were assigned separately to different pressures of oxygen to which it was to be exposed. Lymphocytes from spleen, thymus, and peripheral blood were analyzed following oxygen exposure. Subset populations changed depending on the oxygen tension. Blood lymphocyte populations reflected lymphocyte changes in thymus or spleen. Thus, a full understanding of the pharmacological effects of hyperbaric oxygen, requires a knowledge of simultaneous effects of increased oxygen pressures on the various compartments comprising the immune system.

Signs of cellular immunosuppression correlate with HLA-DR phenotypes in healthy HIV-negative homosexuals: preliminary findings.

Twelve healthy, anal-receptive, homosexual Caucasian males who were seronegative for HIV antibody were typed for HLA-DR antigens. Flow cytometry was used to immunophenotype peripheral blood lymphocytes bearing the CD4, CD8, LEU7, and combined CD8 and LEU7 antigens. These individuals had reported a large number of sexual partners within a five-year period preceding this study. Each individual was assigned a score based on the Hardy-Weinberg frequency of their HLA-DR phenotype in the Caucasian population. The larger the value of this score, the more common the HLA-DR phenotype, the smaller the score, the rarer the phenotype in the population at large. A significant inverse correlation was observed between this score and the proportion of lymphocytes with CD8 and LEU7 antigens. Lymphocytes bearing these two antigens have in vitro suppressor activity and are elevated in patients with human immunodeficiency virus (HIV) infection. The inverse association between CD8+/LEU7+ cells and frequency of HLA-DR phenotypes is consistent with the hypothesis that individuals with rarer phenotypes whose partners are drawn from the population at large are more likely to be challenged during anal insemination, which results in immunosuppression (alloantigenic challenge hypothesis). On the other hand, it is possible that an association exists between certain HLA-DR phenotypes and immune status. Although these observations were made in a very small sample, we believe that the strength of this association provides justification for further investigation into the possibility that alloantigenic challenge may increase the risk for infection, if exposed to HIV, and augment the immunosuppressive action of HIV once significant infection has occurred.

Toxocara canis: failure to find IgE receptors (Fc epsilon R) on eosinophils from infected mice suggests that murine eosinophils do not kill helminth larvae by an IgE-dependent mechanism.

Eosinophils obtained by bronchoalveolar lavage (BAL) from the lungs of mice infected with Toxocara canis were characterized by flow cytometry with respect to cytophilic antibodies and surface Fc receptors. Freshly harvested BAL eosinophils were negative for sIgM, sIgA, sIgE, and Fc epsilon RII. These eosinophils were positive for sIgG1 and Fc gamma RII, although not all Fc gamma RIIs contained bound ligand. Culturing eosinophils for 24 or 48 hr with exogenous IgE and/or IL-4 did not induce IgE binding capacity or Fc epsilon RII expression. IL-4 did not decrease Fc gamma RII expression but did decrease ligand binding capacity by Fc gamma RII. These findings are in marked contrast to the results of studies characterizing the surface of both human and rat eosinophils and may indicate different functional activities for mouse BAL eosinophils in helminth infections.

Intracellular calcium puffs in osteoclasts.

We studied intracellular calcium ([Ca(2+)](i)) in acid-secreting bone-attached osteoclasts, which produce a high-calcium acidic extracellular compartment. Acid secretion and [Ca(2+)](i) were followed using H(+)-restricted dyes and fura-2 or fluo-3. Whole cell calcium of acid-secreting osteoclasts was approximately 100 nM, similar to cells on inert substrate that do not secrete acid. However, measurements in restricted areas of the cell showed [Ca(2+)](i) transients to 500-1000 nM consistent with calcium puffs, transient (millisecond) localized calcium elevations reported in other cells. Spot measurements at 50-ms intervals indicated that puffs were typically less than 400 ms. Transients did not propagate in waves across the cell in scanning confocal measurements. Calcium puffs occurred mainly over regions of acid secretion as determined using lysotracker red DND99 and occurred at irregular periods averaging 5-15 s in acid secreting cells, but were rare in lysotracker-negative nonsecretory cells. The calmodulin antagonist trifluoperazine, cell-surface calcium transport inhibitors lanthanum or barium, and the endoplasmic reticulum ATPase inhibitor thapsigargin had variable acute effects on the mean [Ca(2+)](i) and puff frequency. However, none of these agents prevented calcium puff activity, suggesting that the mechanism producing the puffs is independent of these processes. We conclude that [Ca(2+)](i) transients in osteoclasts are increased in acid-secreting osteoclasts, and that the puffs occur mainly near the acid-transporting membrane. Cell membrane acid transport requires calcium, suggesting that calcium puffs function to maintain acid secretion. However, membrane H(+)-ATPase activity was insensitive to calcium in the 100 nM-1 microM range. Thus, any effects of calcium puffs on osteoclastic acid transport must be indirect.

Counter inhibitor: a low molecular weight cytokine derived from human leukocyte dialysates reverses antigen dependent PMN and macrophage migration inhibition.

A low molecular weight component, termed counter inhibitor (CI), has been partially purified from human dialyzable leukocyte extracts. Addition of CI to either a direct leukocyte or macrophage migration inhibition system results in reversal of antigen-induced migration inhibition. CI activity requires the presence of antigen for expression, but does not require that the donor of the CI be immune to the antigen used in the migration inhibition assay. Reversal of migration inhibition by CI appears to be a consequence of its ability to prevent PMNs or macrophages from responding to lymphokines which induce migration inhibition.

Human squamous cell carcinoma lines express oncofetal 44-kD polypeptide defined by monoclonal antibody to mouse fetus.

Most primary human carcinomas uniformly express an oncofetal epitope which has not been demonstrated previously in established human carcinoma cell lines. We successfully derived several low-passage cell lines of human squamous cell carcinoma (SCC) from head and neck tumors using an in vitro adaptation procedure, characterized these lines, and examined them for expression of a 44-kilodalton (kD) polypeptide (PP) oncofetal antigen (OFA) at the cell surface. Newly established an in vitro-passaged SCC cells retained characteristic microvilli, numerous desmosomes and tonofilaments, abundant rough endoplasmic reticulum, osmophilic keratohyaline granules, and other features of the primary SCC cells. These new cell lines and two long-term, established SCC lines (FaDu and Detroit 562) displayed OFA at the cell surface, as determined by flow cytometry using monoclonal antibody (MoAb) 115. While the FaDu and Detroit 562 lines exhibited aneuploidy during flow cytometric analysis, the new, low-passage SCC lines that we developed remained diploid as were the primary SCC cells from which they were derived. We propose that the expression of a 44-kD OFA is a common feature of human SCC. This marker may prove useful in the detection and treatment of these tumors.

Radiation-induced lymphoblastic lymphomas/leukemias and sarcomas of mice express conserved, immunogenic 44-kilodalton oncofetal antigen.

X-ray-induced, lymphoblastic, T-cell lymphoma/leukemias from irradiated RF mice were observed to uniformly expressed a 44-kd oncofetal antigen (OFA). The OFA polypeptide was detected by flow cytometry, affinity column SDS-PAGE analysis, and immunoblotting with monoclonal antibody (MAb) 115 prepared against syngeneic mouse fetus. X-ray and ultraviolet (UV) induced murine fibrosarcoma cell lines, used as classic models in radiation biology, were also found to express the OFA, which suggested that the 44-kd OFA was a general transformation marker of tumors. Adult mouse thymocytes and other adult tissues expressed no OFA. The 44-kd polypeptide was located at the surface membrane of the tumors examined. In contrast to other reports, lymphoblastic lymphoma cell lines expressed the OFA as a cross-protective, rather than an individually-specific, tumor-associated transplantation antigen. Pronase treatment removed OFA from the surface of living lymphoma cells, whereas collagenase, neuraminidase, and hyaluronidase did not. The OFA was rapidly reexpressed upon culture of the pronase-treated cells. Taken together, these results suggest that the 44-kd OFA polypeptide described here may provide a useful cell surface marker for future radiation carcinogenesis studies. MAb 115 is a promising reagent for detecting tumor-associated 44-kd OFA, for assessing immunoregulatory perturbations to the OFA caused by radiation damage and for investigating the immunopathology of OFA-associated radiation damage.