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A novel class of indole ligands for estrogen receptor alpha have been discovered which exhibit potent affinity and high selectivity. Substitution of the bazedoxifene skeleton to the linker present in the HTS lead 1a provided 22b which was found to be 130-fold alpha-selective and acted as an antagonist of estradiol activity in uterine tissue and MCF-7 cancer cells.

Two novel side chains which had previously been found to enhance antagonist activity in the dihydrobenzoxathiin SERM series were applied to three existing platforms. The novel side chains did not improve the antagonist activity of the existing platforms.

The discovery, synthesis, and SAR of chromanes as ERα subtype selective ligands are described. X-ray studies revealed that the origin of the ERα-selectivity resulted from a C-4 trans methyl substitution to the cis-2,3-diphenyl-chromane platform. Selected compounds from this class demonstrated very potent in vivo antagonism of estradiol in an immature rat uterine weight assay, effectively inhibited ovariectomy-induced bone resorption in a 42 days treatment paradigm, and lowered serum cholesterol levels in ovx’d adult rat models. The best antagonists 8F and 12F also exhibited potent inhibition of MCF-7 cell growth and were shown to be estrogen receptor down-regulators (SERDs).

The ring oxygen and sulfur analogs of lasofoxifene, 1a and 1b, were synthesized in an attempt to impart ERα selectivity, as found in the closely related dihydrobenzoxathiin compound I, recently discovered in these laboratories. The resulting isochroman and isothiochroman compounds were found to exhibit equipotent binding affinities to the ER isoforms and were less active in the inhibition of estradiol-triggered uterine growth when compared to I and lasofoxifene.

A series of dihydrobenzoxathiin SERAMs with alkylated pyrrolidine side chains or alkylated linkers was prepared. Minor modifications in the side chain or linker resulted in significant effects on biological activity, especially in uterine tissue.

Somatostatin (SST) regulates growth hormone (GH) secretion from pituitary somatotrophs by interacting with members of the SST family of G-protein-coupled receptors (sst1-5). We have used potent, nonpeptidyl SST agonists with sst2 and sst5 selectivity to determine whether these receptor subtypes are involved in regulating growth hormone releasing hormone (GHRH) stimulated secretion. GHRH stimulated GH release from pituitary cells in a dose-dependent manner, and this secretion was inhibited by Tyr(11)-SST-14, a nonselective SST analog. A sst2 selective agonist, L-779,976, potently inhibited GHRH-stimulated GH release. In addition, L-817, 818, a potent sst5 receptor selective agonist, also inhibited GH secretion, but was approximately 10-fold less potent (P0.01, ANOVA) in inhibiting GH release than either Tyr(11)-SST-14 or L-779, 976. These results show that both sst2 and sst5 receptor subtypes regulate GHRH-stimulated GH release from rat pituitary cells.

Nonpeptide agonists of each of the five somatostatin receptors were identified in combinatorial libraries constructed on the basis of molecular modeling of known peptide agonists. In vitro experiments using these selective compounds demonstrated the role of the somatostatin subtype-2 receptor in inhibition of glucagon release from mouse pancreatic alpha cells and the somatostatin subtype-5 receptor as a mediator of insulin secretion from pancreatic beta cells. Both receptors regulated growth hormone release from the rat anterior pituitary gland. The availability of high-affinity, subtype-selective agonists for each of the somatostatin receptors provides a direct approach to defining their physiological functions.

A series of nonpeptide somatostatin agonists which bind selectively and with high affinity to somatostatin receptor subtype 2 (sst2) have been synthesized. One of these compounds, L-054,522, binds to human sst2 with an apparent dissociation constant of 0.01 nM and at least 3,000-fold selectivity when evaluated against the other somatostatin receptors. L-054,522 is a full agonist based on its inhibition of forskolin-stimulated adenylate cyclase activity in Chinese hamster ovary-K1 cells stably expressing sst2. L-054,522 has a potent inhibitory effect on growth hormone release from rat primary pituitary cells and glucagon release from isolated mouse pancreatic islets. Intravenous infusion of L-054,522 to rats at 50 μg/kg per hr causes a rapid and sustained reduction in growth hormone to basal levels. The high potency and selectivity of L-054,522 for sst2 will make it a useful tool to further characterize the physiological functions of this receptor subtype.

Dihydrobenzodithiin compounds (1-6) were prepared to explore the expansion of the dihydrobenzoxathiin lead compounds I-III as SERAMs (Selective Estrogen Receptor Alpha Modulators). The dihydrobenzodithiin compounds generally maintained a high degree of selectivity for ERalpha over ERbeta, however, they lacked the in vivo antagonism/agonism activity exhibited by the lead class in an immature rat uterine growth model.

High affinity avermectin binding sites have been identified and partially characterized in membranes from two insect species, Drosophila melanogaster and the locus Schistocerca americana. There is a 10-fold increase in the density of ivermectin binding sites associated with membranes isolated from Drosophila heads (a neuronally enriched tissue source) compared to the bodies (Bmax values were 3.5 and 0.22 pmol/mg, respectively) with only a small difference in the apparent dissociation constant (Kd values of 0.20 and 0.34 nM for heads and bodies, respectively). Membranes prepared from metathoracic ganglia of the locust, Schistocerca americana, were highly enriched in high affinity avermectin binding sites (Kd = 0.2 nM and Bmax = 42 pmol/mg). Using an [125I]arylazido-avermectin analog as a photoaffinity probe, a 45 kDa protein was identified in both the Drosophila head and body tissue preparations. A 45 kDa protein was also specifically labeled with [125I]azido-avermectin in the locust neuronal membranes.

Estrogen acts through two molecularly distinct receptors termed estrogen receptor alpha (ERα) and estrogen receptor beta (ERβ) which bind estradiol with similar affinities and mediate the effects of estrogen throughout the body. ERα plays a major role in reproductive physiology and behavior, and mediates classic estrogen signaling in such tissues as the uterus, mammary gland, and skeleton. ERβ, however, modulates estrogen signaling in the ovary, the immune system, prostate, gastrointestinal tract, and hypothalamus, and there is some evidence that ERβ can regulate ERα activity. Moreover, ERβ knockout studies and receptor distribution analyses in the CNS suggest that this receptor may play a role in the modulation of mood and cognition. In recent years several ERβ-specific compounds (selective estrogen receptor beta modulators; SERM-beta) have become available, and research suggests potential utility of these compounds in menopausal symptom relief, breast cancer prevention, diseases that have an inflammatory component, osteoporosis, cardiovascular disease, and inflammatory bowel disease, as well as modulation of mood, and anxiety. Here we demonstrate an antidepressant-like effect obtained using two SERM-beta compounds, SERM-beta1 and SERM-beta2. These compounds exhibit full agonist activity at ERβ in a cell based estrogen response element (ERE) transactivation assay. SERM-beta1 and 2 are non-proliferative with respect to breast as determined using the MCF-7 breast cancer cell-based assay and non-proliferative in the uterus as determined by assessing the effects of SERM-beta compounds on immature rat uterine weight and murine uterine weight. In vivo SERM-beta1 and 2 are brain penetrant and display dose dependent efficacy in the murine dorsal raphe assays for induction of tryptophan hydroxylase mRNA and progesterone receptor protein. These compounds show activity in the murine forced swim test and promote hippocampal neurogenesis acutely in rats. Taken together these data suggest that ERβ may play an important role in modulating mood and the ERβ specific compounds described herein will be useful tools for probing the utility of an ERβ agonist for treating neuroendocrine-related mood disturbance and menopausal symptoms.

Avermectin-binding proteins from the free-living nematode worm Caenorhabditis elegans and from the fruitfly Drosophila melanogaster were purified to homogeneity via a three-step procedure. The binding proteins were covalently labelled using a radioactive photoaffinity probe and then partially purified on a Sephacryl S-300 gel-filtration column. The radiolabelled binding proteins were then purified by immunoaffinity chromatography using a monoclonal antibody to avermectin covalently attached to Protein A-Sepharose beads. Three affinity-labelled Drosophila proteins with molecular masses between 45 and 50 kDa were isolated in this way and then separated from each other by electroelution. This three-step protocol provides a rapid technique for receptor purification which may be of use in the purification of other binding proteins.

The design and synthesis of a series of avermectin affinity probes used in the identification and purification of the avermectin binding proteins is described. These modified avermectins fall into two design classes: ligands to covalently modify specific avermectin binding proteins [an 125I-labeled aryl azide photoprobe (15) and a tritiated aziridine analog (6)] and ligands for affinity chromatography applications [three biotinylated compounds (10, 12, and 13) and one resin-bound derivative (9)]. The binding affinities of these compounds for the Caenorhabditis elegans avermectin binding protein is presented as well as their biological activities against C. elegans and Artemia salina.

Synthesis and derivatization of a series of substituted tetrahydrofluorenone analogs giving potent, ERbeta subtype selective ligands are described. Several analogs possessing ERbeta binding affinities comparable to 17beta-estradiol but with greater than 75-fold selectivity over ERalpha are reported.

The effects of estrogen receptor (ER) ligands on the stability and transcriptional activity of ERbeta in the breast cancer cell lines MCF-7 and HeLa were examined. We found that ERbeta was degraded in the presence of 17beta-estradiol. Tamoxifen and Faslodex (ICI 182,780) prevented ERbeta receptor destabilization. In contrast to ERalpha, ERbeta degradation was not abolished by inhibitors of the proteasome-mediated protein degradation pathway. Furthermore, single point mutations in helix 12 of the receptor dramatically affected the stability and subsequent transcriptional activation of ERbeta.

A series of benzoxathiin SERAMs with heteroatom-substituted amine side chains was prepared. Minor modifications in the side chain resulted in significant effects on biological activity, especially in uterine tissue.

A series of benzoxathiin SERAMs with bicyclic amine side chains was prepared. Minor modifications in the side chain resulted in significant effects on biological activity, especially in uterine tissue.

Dihydrobenzoxathiin analogs (1-11) with modifications on the basic side chain region were prepared and evaluated for estrogen/anti-estrogen activity in both in vitro and in vivo models. The compounds generally maintained a high degree of selectivity for ERalpha over ERbeta, similar to the original lead compound I. Many of the compounds also maintained high potency in the inhibition of human carcinoma MCF-7 cell growth. However, all were less potent in the inhibition of estradiol-triggered uterine growth. This work demonstrates the sensitive nature of modification to the antagonist basic side chain region.

Somatostatin, also known as somatotropin release-inhibiting factor (SRIF), is secreted by pancreatic delta-cells and inhibits the secretion of both insulin and glucagon. SRIF initiates its actions by binding to a family of six G protein-coupled receptors (sst1, -2A, -2B, -3, -4, and -5) encoded by five genes. Messenger RNA for both sst2 and sst5 have been reported in the rat pancreas, and the sst2A receptor protein has been localized to rat pancreatic alpha and pancreatic polypeptide-secreting cells in the islets as well as to pancreatic acinar cells. In this study we have used double immunostaining to show that the sst5 protein is expressed exclusively in the beta-cells of rat pancreatic islets and localizes with insulin-secreting alpha-cells. The sst5 receptor is not colocalized with sst2A. Thus, in the rat SRIF inhibits pancreatic insulin and glucagon secretion via different sst receptor subtypes.

An azido-avermectin analog [4'' alpha-(4-azidosalicylamido-epsilon-caproylamido-beta-alan ylamido)-4''-deoxyavermectin B1a; azido-AVM] was synthesized and used to photoaffinity label avermectin binding sites present in the membranes of Caenorhabditis elegans and Drosophila melanogaster. Azido-AVM was biologically active and behaved like a competitive inhibitor of [3H]ivermectin binding to C. elegans membranes (Ki = 0.2 nM). Radiolabeled azido-AVM bound specifically and with high affinity to C. elegans membranes (Kd = 0.14 nM) and, upon photoactivation, became covalently linked to three C. elegans polypeptides of 53, 47, and 8 kDa. Photoaffinity labeling of a membrane preparation from D. melanogaster heads resulted in labeling of a single major polypeptide of approximately 47 kDa. The proteins that were covalently tagged in these experiments are believed to be associated with avermectin-sensitive chloride channels present in the neuromuscular systems of C. elegans and D. melanogaster. Azido-AVM did not bind to rat brain membranes and therefore was selective for the nematode and insect receptors.

Sera from patients exposed to measles virus were investigated for the presence of antibodies against each of the viral antigens. All sera with measurable neutralizing titers contained antibodies against the two surface proteins (the glycoprotein and fusion protein), the nucleocapsid protein, and one of the internal proteins (P2). However, only sera from individuals with clinical symptoms of measles infection (natural measles and atypical measles) contained antibodies against the measles virus matrix protein. Levels of matrix-specific antibodies were highest in patients with atypical measles infection.

Purified human lung mast cells released histamine, leukotrienes, prostaglandin (PG) D2, thromboxane B2 (TxB2), and PGF2 alpha in response to anti-IgE stimulation. Incubation of the cells for 24 h with 10(-6) M dexamethasone, a treatment that inhibits mediator release from human basophils, had no effect on the release of these mediators from mast cells. Dexamethasone treatment of human lung fragments led to little or no inhibition of anti-IgE-induced release of the mast cell-derived mediator, histamine, but produced a significant inhibition of the release of PGE2, PGF2 alpha, and 6-keto-PGF1 alpha. As was the case with purified mast cells, the steroid did not inhibit the release of PGD2 or TxB2 from human lung fragments. Comparison of the quantities of PGD2 and TxB2 produced by purified cells and human lung fragments reveals that the mast cells produce quantities of these metabolites sufficient to account for the entire amount produced by challenged lung fragments. Dexamethasone inhibited spontaneous release from lung fragments of all cyclooxygenase products measured. These results suggest that the human lung parenchymal mast cell phospholipase is not inhibited by dexamethasone, whereas other phospholipase(s) in the lung are inhibited by the steroid. These results may be useful in explaining the resistance of acute allergic reactions, including anaphylaxis, to steroids, despite the potent antiinflammatory activity of steroids on subacute and chronic inflammation, such as in bronchial asthma, which may be initiated by IgE-dependent mechanisms.

Receptor binding proteins of Treponema pallidum were identified by incubation of [35S]methionine-labeled, soluble T. pallidum preparations with formaldehyde-fixed HEp-2 cells. Three major treponemal proteins (bands 1--3) that avidly bound to the eucaryotic cell surface were detected by sodium dodecylsulfate-polyacrylamide gel electrophoresis and fluorography. Brief trypsin treatment of HEp-2 cells before formaldehyde fixation reduced the extent of the interaction of these treponemal macromolecules, which implicated receptor-mediated attachment mechanisms. The presence of unlabeled T. pallidum preparations directly competed with radiolabeled T. pallidum samples for the available HEp-2 cells, which suggested a limiting number of membrane binding sites. Samples of unlabeled avirulent Reiter treponeme did not compete. T. Pallidum immunogens were examined by radioimmunoprecipitation with human and rabbit syphilitic sera. Of interest were the similarities and extent of the humoral response represented by the detection of antigen-antibody complexes against numberous treponemal proteins, including bands 1--3. T. pallidum portein band 1 appeared to be the major antigenic stimulus. Formation of antigen-antibody complexes between 35S-labeled T. pallidum proteins and human syphilitic sera was prevented by unlabeled T. pallidum but not by T. phagedenis preparations, which demonstrated specificity of the reaction. Gel profiles of radioimmunoprecipitation assays using radiolabeled T. pallidum antigens and human syphilitic and yaws sera delineated both the similarities and differences in the humoral response to these two spirochetes. The latter suggested both overlapping and distinguishing antigenic properties between T. pallidum and T. pertenue. Detection in yaws sera of specific antibody against T. pallidum protein bands 1--3 further incriminates the role of these three treponemal proteins as virulence determinants.

Platelet-activating factor (PAF) and leukotrienes, newly described classes of vasoactive lipids, may play a role in anaphylaxis. It has recently been suggested that the vasoconstrictor effects of PAF in isolated rat lung are related to release of leukotrienes C4 and D4. Thyrotropin-releasing hormone (TRH), a tripeptide, has potent antihypotensive activity in experimental shock, including that resulting from either leukotriene D4 administration or antigen-induced anaphylaxis. We utilized an unanesthetized guinea pig model to study the relationships among PAF, leukotrienes, and TRH and their potential interactions on the cardiovascular system. PAF (1 nmol/600 g body weight i.v.) produced profound hypotension which was completely blocked by TRH (2 mg/kg i.v.). Nafazatrom or FPL 55712, a presumed receptor antagonist of leukotrienes, was ineffective, whereas U-60257, a leukotriene synthesis inhibitor, displayed incomplete blockade. Moreover, leukotriene-like immunoreactivity in plasma did not increase following PAF administration. Thus, hypotension produced by PAF does not appear to result secondarily from release of cysteinyl leukotrienes. Moreover, the ability of TRH to block the hypotensive effects of PAF may partially account for its beneficial effects in experimental anaphylaxis and provides further rationale for the therapeutic evaluation of this peptide in anaphylactic shock.

Using immunoprecipitation techniques, we have analyzed measles-specific antibodies in the cerebrospinal fluids (CSF) as well as in sera from patients with subacute sclerosing panencephalitis (SSPE). We confirm previous reports that SSPE sera contain a relative lack of M protein-specific antibodies, and report that CSF also have antibodies specific for all measles polypeptides except the M protein. We have also found that Vero cells infected with one of the SSPE viruses used in this study, the cell-associated IP-3 strain, completely lack expression of detectable M protein. Thus, the lack of M protein-specific antibody in the CSF of SSPE patients may be the result of a lack of expression of this polypeptide in the cells of the central nervous system.

The increased capacity of lymphocytes from patients with multiple sclerosis to adhere to human epithelial cells persistently infected with measles virus has provided an accurate blood test for multiple sclerosis. When lymphocytes from affected patients were mixed with measles-infected human epithelial cells, the lymphocytes formed rosettes around a mean (±S.E.) of 69.2±1.7 per cent of the measles-infected cells. In contrast, lymphocytes from controls, either healthy or with other neurologic and non-neurologic diseases, formed rosettes around a mean of only 28.2 ± 2.1 per cent of the measles-infected cells. Of greater importance was the complete absence of overlap between multiple sclerosis and control values, thus indicating the diagnostic potential of the rosetting phenomenon. The severity, duration and activity of the disease had no effect on the degree of rosette formation. (N Engl J Med 294:1423–1427, 1976)

Nineteen hybridoma cell lines derived from the spleen cells of a mouse immunized with reovirus serotype 3 (strain Dearing) were cloned and the IgGs secreted by them characterized. Four of the IgGs were directed against polypeptide μNS and two against polypeptide σNS, the two nonstructural reovirus-specified polypeptides. Two IgGs were directed against polypeptide λ2 and two against polypeptide σ2, both components of the reovirus inner capsid shell. Four IgGs were directed against polypeptide σ1, the most type specific of all reovirus-specified polypeptides, three against polypeptide μl/gmlC and one against polypeptide σ3, all of them components of the reovirus outer capsid shell. One IgG was directed against a complex composed of polypeptides μl/gmlC and σ3, but failed to react with either of these polypeptides alone. Thus the 19 hybridoma cell lines secreted IgGs with specificities for 7 of the 10 reovirus-specified proteins. The ability of all these IgGs to precipitate the proteins specified by the two heterologous reovirus serotypes, serotypes 1 and 2, was also measured.

Viral polypeptides in extracts prepared from [35S]methionine-labeled human epithelial carcinoma cells persistently infected with measles virus were reacted with virus-specific antisera. Microcolumns of staphylococcal protein A linked to Sepharose were used to isolate antigen-antibody complexes that contained few contaminating host polypeptides. Measles virus polypeptides in these complexes could be identified readily on sodium dodecyl sulfate-polyacrylamide gels even when antiserum with low reactivity toward the viral antigens was used.

Nucleocapsids in quantities approaching 1 mg were purified from 109 measles virus-infected cells. They contained one polypeptide species with a molecular weight of 59,000. Antiserum was raised in rabbits against purified nucleocapsids and used in a competitive radioimmunoassay. Because of their instability, purified nucleocapsids were not suitable for use in such an assay. Instead partially purified nucleocapsids from HEp-2 cells persistently infected with measles virus and labeled in vitro with [35S]methionine were used as the source of radioactive antigen. The radioimmunoassay thus developed measured less than 5 ng of nucleocapsids in infected cells.

Immunoprecipitation methods were used to analyze sera and cerebrospinal fluids from patients with multiple sclerosis for measles virus-specific antibodies. The sera contained antibodies against all virus antigens except the matrix polypeptide. Of the nine cerebrospinal fluids investigated, two contained undetectable levels of measles-specific antibodies, four contained antibodies against the nucleocapsid and another internal antigen, and three contained antibodies against the surface antigens as well as the internal antigens.

Radioimmunoassays for 5(S), 12(R)-dihydroxyeicosa-6, 14-cis, 8,10-trans-tetraenoic acid (leukotriene B4, LTB4) and 5(S)-hydroxy-6(R)-L-gamma-glutamyl-L-cysteinyl-glycinyleicosa-7,9- trans, 11,14-cis-tetraenoic acid (leukotriene C4, LTC4) have been used to quantify the concentrations of these arachidonic acid metabolites in plasma (12 patients) and blister fluid (6 patients) of burned patients. The results of this study demonstrate that, in general, burn plasma LTB4, and LTC4 were not elevated; however, in individual cases, transient high levels of leukotrienes were observed. Correlation between leukotriene "peaks" and the clinical course could not be established. High levels of LTB4 and LTC4 in burn blister fluid suggest their participation in local inflammatory reactions.

Radlolmmunoassays for Ieukotriene C 4 (LTC 4 ) end for Ieukotriene B 4 (LTB 4 ) have been developed. LTC 4 was conjugated with thiolated hemocyanin (Keyhole Limpet) (KLH) using 6-(N-maielmido)hexanoic acid chloride as coupling agent. LTB 4 was converted to its hydrazide derivative, via the δ-lactone and the hydrazide was similarly coupled with thiolated KLH using 6-(N-maleimido)hexenolc acid chloride as coupling agent. These conjugates were used to consistently raise high titres of anti-leukotriene antibody in rabbits. 14,15-[ 3 H]-LTC 4 was prepared by total synthesis via two routes, 14,15-[ 3 H]-LTB 4 was prepared by total synthesis. The assay for LTC 4 recognizes LTC 4 , LTD 4 and LTF 4 , and to a lesser extent, LTE 4 with a detection limit of ca. 0.1 pmoIes LTC 4 per. ml. of sample. The assay for LTB 4 is highly specific and has a similar detection limit.

A procedure using high performance liquid chromatography (HPLC) is described for the separation of major primary cyclooxygenase metabolites (prostacyclin metabolite-6ketoPGF1α, thromboxane B2, and prostaglandins F2α, E2, and D2), leukotrienes (C4, B4, and D4), monohydroxyeicosatetraenoic acids (15-, 11-, 12-, and 5HETEs), and free arachidonic acid. It is therefore possible to quantitate major arachidonic acid metabolites by a single chromatographic procedure. Using this technique we have determined that a major arachidonic acid metabolite of human lung macrophages co-elutes with leukotriene B4.

Enzyme-linked immunosorbent assays (ELISAs) were developed for the leukotrienes LTC4 and LTB4 and the prostaglandins 6-keto PGF1 alpha and thromboxane (TxB2). In an indirect assay procedure for all 4 eicosanoids a BSA conjugate of the leukotrienes or an ovalbumin conjugate of the prostaglandins was absorbed to polystyrene microtiter plates. Samples containing the respective eicosanoids were incubated in the coated wells with specific rabbit antisera. The wells were then incubated successively with a goat anti-rabbit antibody linked to fluorescein and a rabbit anti-fluorescein antibody linked to alkaline phosphatase. The resultant assays for LTC4, LTB4, 6-keto PGF1 alpha, and TxB2, gave steep, sensitive inhibition curves; IC50s were 0.2, 10, 1, and 0.4 pmol respectively with minimal cross-reactivity to other eicosanoids. The sensitivities and specificities were comparable to those found in the RIA, and the levels determined in this assay correlate well with those determined in non-immunological assays.

ECHOvirus 33 isolated from the cerebrospinal fluid of a patient with agammaglobulinemia was shown to replicate in vitro in peripheral leukocyte suspensions from a normal antibody negative donor. Replication was demonstrated by use of sequential dilution experiments. Washed glass adherent mononuclear cell cultures from a normal antibody negative donor were also capable of supporting ECHOvirus 33 replication in vitro. Leukocyte suspensions from the infected agammaglobulinemic patient extinguished detectable infectious virus in vitro.

We have recently described the isolation of 19 hybridoma cell lines that secrete IgGs directed against reovirus-coded proteins, and characterized their specificities as judged by their ability to precipitate virus-coded proteins from lysates of infected cells. We describe in this paper the characterization of these hybridoma-secreted IgGs by their ability to react with reovirus particles. IgGs directed against three reovirus proteins were able to neutralize infectivity, inhibit hemagglutination, and precipitate/aggregate reovirus particles: those directed against polypeptides σ1 and σ3, both components of the outer reovirus capsid shell, and those directed against polypeptide λ2, a component of reovirus cores. In addition, some, but not all, of the IgGs directed against polypeptides μ1/μ1C and μNS also precipitate/aggregate reovirus particles. The fact that IgGs directed against λ2 possess strong neutralizing, hemagglutination inhibiting, and virus precipitating activities suggests that the projections or spikes that are present on reovirus cores and that are composed primarily or exclusively of λ2 project through the outer capsid shell to the surface of reovirus particles. This conclusion was confirmed by the demonstration that polypeptide λ2 could be labeled by means of the lactoperoxidase-catalyzed radioiodination technique under conditions when only known components of the reovirus outer capsid shell became labeled.

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