Faculty Bibliography

Muramyldipeptide (MDP) and murabutide (MB) suppressed hapten-specific IgE antibody-forming cell (AFC) responses in vivo. IgE responses were induced in BALB/c mice by intraperitoneal injection with benzylpenicilloyl-keyhole limpet hemocyanin (BPO-KLH) (10 micrograms) in aluminum hydroxide gel (Alum) on days 0, 21 and 42. On day 44, mice were fed (gavage) or injected subcutaneously with varying concentrations of MDP or MB (0.1-500 mg/kg). The mice were killed on days 45-70, and the numbers of BPO-specific IgM, IgG1, IgE, and IgA AFC in various lymphoid organs were determined in an enzyme-linked immunosorbent spot (ELISPOT) assay. In addition, levels of BPO-specific IgE in serum were determined by ELISA. Data are expressed as AFC/10(7) cells or as micrograms/ml. Feeding with MDP or MB on day 44 suppressed BPO-specific IgE AFC responses and serum levels of BPO-specific IgE within 48 h (day 46) (65-100% and approximately 50% decrease, respectively). With both molecules, the suppression was IgE isotype-specific, dose-dependent and transient. The suppression was also route-specific since it was obtained only when MDP or MB were given by gavage, and not when injected subcutaneously. These results show that peak antigen-specific IgE responses can be downregulated in vivo, in isotype-specific fashion, by a clearly defined class of molecules, MDP and MB, one of which, MB, is a candidate for clinical studies in man. The mechanism of suppression probably involves the modulation of gut-associated lymphoid tissue and mucosal immunity. The clinical implications are that pharmacologic agents of this type may be suitable for use in the therapeutic or prophylactic downregulation of IgE and, hence, in the therapy of IgE-mediated diseases in man such as allergic rhinitis, asthma, and other atopic diseases

The effect of the substitution of Arg for Gly 13 on the structure of the transforming region decapeptide (Leu 6-Gly 15) of the ras oncogene encoded P21 protein has been investigated using conformational energy analysis. A human malignancy has been identified that contains a ras gene with a single mutation in the thirteenth codon such that the encoded protein would have Arg substituted for Gly at this position, and transfection of cells in culture with this gene results in malignant transformation. Conformational analysis demonstrates that the Arg 13 decapeptide adopts a conformation identical to that for other peptides with substitutions at position 13 (Asp 13, Val 13) from transforming proteins that is distinctively different from that for peptides (Gly 13, Ser 13) from normal, nontransforming proteins. This is found to be an indirect effect resulting from changes in the conformation of Gly 12 produced by substitutions at position 13. These results are consistent with recent analysis of crystallographic data of proteins on conformational preferences for glycine in tripeptide sequences.