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IgM exists as both a monomer on the surface of B cells and a pentamer secreted by plasma cells. Both pre-immune "natural" and antigen-induced "immune" IgM antibodies are important for protective immunity and for immune regulation of autoimmune processes by recognizing pathogens and self-antigens. Effector proteins interacting with the Fc portion of IgM, such as complement and complement receptors, have thus far been proposed but fail to fully account for the IgM-mediated protection and regulation. A major reason for this deficit in our understanding of IgM function seems to be lack of data on a long elusive Fc receptor for IgM (FcμR). We have recently identified a bona fide FcμR in both humans and mice. In this article we briefly review what we have learned so far about FcμR.

Thirty wether lambs were randomly assigned to three treatments consisting of a control (C) and two vitamin E-supplemented treatments (VE), one fed 500 IU of vitamin E.lamb -1 .d -1 (E500) and the other fed 1,000 IU of vitamin E.lamb -1 .d -1 (E1000). After a 56-d feeding period, lambs were slaughtered and carcass traits were evaluated. Whole-sale legs and loins were vacuum-packaged, stored at 4 o C for 7, 14, 21, or 28 d, fabricated into retail cuts, and packaged and displayed to simulate retail industry conditions. The E1000 lambs gained less (P

Stimulation of the amygdala in rats is known to elicit increases in heart rate (HR) and blood pressure (BP) as well as locomotor activity associated with emotional arousal. The present study was conducted to localize and characterize the role of the GABA system of the amygdala in regulating these cardiovascular responses. Male Sprague-Dawley rats with arterial catheters placed for physiological measurements were implanted with chronic microinjection cannulae in the anterior basolateral (BLA) and central (Ce) amygdaloid nuclei under pentobarbital anesthesia. After recovering, rats were microinjected bilaterally with saline (250 nl) and bicuculline methiodide (BMI, 5-25 ng/250 nl), a selective GABAA antagonist. Microinjection of BMI in the BLA caused significant increases in HR and BP as well as locomotor stimulation while saline had no effect. The cardiovascular response to BMI was blocked by pentobarbital anesthesia. Microinjection of equimolar concentrations of (+)-baclofen HCl (GABAB agonist), phaclofen (GABAB antagonist), or strychnine (glycine antagonist) into the BLA or BMI into the Ce had no significant cardiovascular effects. The cardiovascular effects of BMI injection in the BLA does not appear to be secondary to generalized seizure activity. These results suggest that endogenous GABA, acting on GABAA receptors in the region of the BLA, may be involved in cardiovascular regulation.

The T cell co-receptor, CD8, binds to the alpha 3 domain of HLA class I (Salter, R.D., R.J. Benjamin, P.K. Wesley, S.E. Buxton, T.P.J. Garrett, C. Clayberger, A.M. Krensky, A.M. Norman, D.R. Littman, and P. Parham. 1990. Nature [Lond.]. 345:41; Connolly, J.M., T.A. Potter, E.M. Wormstall, and T.H. Hansen. 1988. J. Exp. Med. 168:325; and Potter, T.A., T.V. Rajan, R.F. Dick II, and J.A. Bluestone. 1989. Nature [Lond.]. 337:73). To identify regions of CD8 that are important for binding to HLA class I, we performed a mutational analysis of the CD8 molecule in the immunoglobulin (Ig)-like variable domain. Our mutational analysis was based on our finding that using a cell-cell adhesion assay murine CD8 (Lyt-2) did not bind to human class I. Since the interaction of human CD8 with HLA class I is species specific, we substituted nonconservative amino acids from mouse CD8 and analyzed the ability of the mutated CD8 molecules expressed in COS 7 cells to bind HLA class I-bearing B lymphoblastoid cells, UC. Mutants with the greatest effect on binding were located in a portion of the molecule homologous to the first and second hypervariable regions of an antibody combining site. In addition, a panel of 12 anti-CD8 monoclonal antibodies were used to stain the 10 CD8 mutants, and amino acids that affected antibody binding were localized on the crystal structure of the Bence-Jones homodimer, REI. Support for an Ig-like structure of CD8 can be found in the pattern of substitutions affecting antibody binding. This work supports the similar tertiary structure of the CD8 alpha-terminal domain and an Ig variable domain.

Feeder steers (n = 84) were stratified into four weight groups to provide slaughter groups so that product that had been in vacuum packages at 0 to 2 degrees C for 40, 60, 80, or 100 d postmortem could be simultaneously evaluated. Each of the four groups was randomly divided into three subgroups so that vitamin E could be supplemented in the diet at rates of 0, 1,000, or 2,000 (E0, E1000, and E2000, respectively) IU.steer-1.d-1 for 100 d. After slaughtering, chilling, and fabricating, one ribeye-roll and one strip loin from each carcass was transported to the university laboratory for analyses, whereas the paired subprimals were transported to Japan. Based on metmyoglobin formation and lipid oxidation, strip loin steaks deteriorated at a faster rate during retail-display than did ribeye steaks. Steaks from subprimals that were stored for 100 d had inferior (P.05) retail-display characteristics and a shorter (P.05) caselife than steaks from the other storage periods. alpha-Tocopherol levels in longissimus muscle were lower (P.05) for E0 than for E1000 and E2000 (3.51, 5.54, and 6.10 micrograms/g of tissue, respectively). Supplementing cattle with vitamin E resulted in steaks that exhibited superior lean color, less surface discoloration, more desirable overall appearance, and less lipid oxidation during retail display than control steaks; minimal differences were observed between E1000 and E2000 steaks. Steaks from cattle supplemented with vitamin E were preferred over control steaks by 91% of Japanese survey participants (n = 10,941), and 58% of all participants identified muscle color as the most important factor in selecting beef products.

Blockade of GABAergic inhibition in the region of the anterior basolateral amygdala (BLA) of rats elicits physiologic changes associated with a defense reaction. The present study was undertaken to determine whether GABA receptors in the BLA might be involved in regulating experimental anxiety using the social interaction (SI) and conflict test. Guide cannulae were stereotaxically implanted bilaterally in the BLA of rats for intracerebral microinjections. In the BLA, injection of the GABAA receptor antagonists bicuculline methiodide (BMI) and picrotoxin (PIC) produced anxiogenic-like effects in the SI paradigm, as did BMI injection using the conflict paradigm. Injection of the GABAA agonist muscimol (MUS) into the central nucleus of the amygdala (Ce) produced anxiolytic-like effects in the SI test. Microinjection of MUS, baclofen (GABAB agonist), 2OH-saclofen (GABAB antagonist) or strychnine (glycine antagonist) into the BLA or BMI into the Ce elicited no change in experimental anxiety as measured by the SI test. These results suggest that endogenous GABA acts tonically at GABAA receptors in the BLA to inhibit anxiety responses.

Blockade of GABAA receptor function in the area of the anterior basolateral amygdala of rats elicits physiological (increases in heart rate and blood pressure) and behavioral changes similar to symptoms of human anxiety states. Repeated subthreshold blockade of GABAA receptors in this region appears to result in a long-term 'priming' of these anxiety-like responses. The present study was conducted to characterize the 'priming' of the heart rate and blood pressure responses and to test if these 'primed' animals would show increases in anxiety responses. Male Wistar rats with arterial catheters placed for physiological measurements were implanted with chronic microinjection cannulae in the anterior basolateral amygdaloid nucleus (BLA) under pentobarbital anesthesia. Repeated daily injections of a subthreshold dose of bicuculline methiodide (GABAA receptor antagonist; BMI) into the BLA elicited 'priming' of physiological responses after 3-5 injections and this response was maintained for at least 6 weeks. The primed animals also showed increased anxiogenic responses to GABAA blockade in the BLA. The 'priming' of anxiety responses were clearly elicited before kindling of seizures as measured by EEG. These results suggest that this 'priming' phenomenon may be similar to kindling and long-term potentiation. This could be one potential mechanism for developing pathological emotional responses, such as chronic, high levels of anxiety.

The amygdala is a structure that is often implicated in the regulation of anxiety responses. Many studies have shown that injection of benzodiazepines into the amygdala produces an anxiolytic effect. The present study was undertaken to determine whether the anxiolytic effect of administration of systemic benzodiazepine (chlordiazepoxide) might be blocked by local injection of a benzodiazepine receptor antagonist (flumazenil) or GABAA receptor antagonist (bicuculline methiodide; BMI) into the region of the anterior basolateral amygdala (BLA) of rats using an ethologically based test of anxiety, the social interaction test. Injection of flumazenil or BMI into the BLA of rats was found to reverse the anxiolytic effects of peripherally administered chlordiazepoxide. These results suggest a major role for the BLA in mediating the anxiolytic effects of benzodiazepines.

The present report provides evidence that whole goat anti-human immunoglobulin, unlike similar reagents produced in the rabbit, binds both to the same number of and the same individual cells as the F(ab')2 fragments of rabbit or goat anti-human immunoglobulin. These results suggest that goat IgG has a lower affinity for the Fc receptors of human lymphocytes and monocytes than rabbit IgG. Because of this property, whole goat antibodies against human immunoglobulin can be used as simple, convenient relatively inexpensive reagents for the routine detection of immunoglobulin on cell surfaces by immunofluorescence microscopy. The preparation of F(ab')2 fragments of anti-immunoglobulin, which are necessary when rabbit antibodies are used, does not appear to -e required if goat antibodies can be empolyed. This observation has multiple practival applications in cellular immunology.