Only multimers of a synthetic peptide of human apolipoprotein E are biologically active

Plasma apolipoprotein E (apoE) is a ligand for the cellular uptake of cholesterol-rich plasma lipoproteins. ApoE also inhibits mitogen-stimulated lymphocyte proliferation and gonadotropin-stimulated ovarian theca/interstitial cell androgen production. To address the mechanism(s) by which apoE is active and to understand its interaction with the target cells, we prepared and examined the inhibitory activity of a series of apoE synthetic peptides. ApoE peptides representing amino acid residues 93-112, 141-155, 161-171, 172-182, and 174-193 were not active in either bioassay. However, specific inhibition of both lymphocyte proliferation and ovarian androgen production was observed with a self-conjugate of peptide-(141-155). Furthermore, a synthesized dimeric peptide representing two repeats of sequence-(141-155) (i.e. (141-155)-(141-155] was active as well. In both bioassays, the inhibition observed was not a result of direct cell killing. Furthermore, these apoE peptides exhibited activities with characteristics that were shared with those of native apoE. The results indicate that amino acid residues 141-155 of apoE are responsible for the biological activity of apoE. Furthermore, the results suggest that dimers or multimers of native apoE may be a biologically important species.     

Immunogenicity of homologous low density lipoprotein after methylation, ethylation, acetylation, or carbamylation: generation of antibodies specific for derivatized lysine

We previously showed that immunization of guinea pigs with reductively glucosylated guinea pig low density lipoprotein (LDL) or albumin resulted in the formation of antibodies specific for the glucosylated protein. The present studies were done to determine if modifications of homologous LDL or albumin, other than addition of carbohydrate, would also render these proteins immunogenic. We found that derivatization of lysine residues of guinea pig LDL or albumin by carbamylation, acetylation, ethylation, or even methylation rendered them immunogenic in guinea pigs. In addition, the specificity of the antibodies was strikingly influenced by whether modified homologous LDL or modified homologous albumin was used as the immunogen. Antibodies generated against modified LDL were directed almost exclusively against the derivatized lysine residues (i.e., carbamyllysine, acetyllysine, or methyllysine) and hence reacted equivalently with other modified proteins that contained the same lysine derivative. However, antibodies generated against guinea pig albumin (or fibrinogen) modified in the same ways reacted primarily with the modified protein used as immunogen, and not with the free lysine derivative, or with other similarly modified proteins. Each of the modifications referred to above could potentially occur in vivo. Therefore, the findings presented may be relevant to autoantibody formation and immunopathogenetic mechanisms in certain diseases.     

Monoclonal antibody detects Ag polymorphism of apolipoprotein B

A monoclonal antibody (MB-19) was used to investigate the polymorphism of apolipoprotein B in a large family and in unrelated subjects. Apolipoprotein B was shown to exhibit high-, intermediate- or low-affinity binding to this antibody. Thus, MB-19 bound strongly to the Ag(c) epitope, An Ag antigenic domain previously characterized by human antisera, while it bound only weakly to the allelic epitope Ag(g). It proved therefore useful for the detection of the two corresponding allelic apoB species designated apoBc (high-affinity binding) and apoBg (low-affinity binding), and for confirming their co-dominant transmission. Intermediate binding resulted from the presence of a mixture of both apoB populations in heterozygous subjects.     

Early Stages of Conjugation in Escherichia coli

We initiated these studies to learn more about the initial events during bacterial conjugation and to optimize conditions for their occurrence. We found that cells in donor cultures grown anaerobically prior to mating have (i) a higher mean number of F pili per cell, (ii) longer F pili, (iii) a higher probability of forming specific pairs with F(-) cells, and (iv) a faster rate of initiation of chromosome transfer than cells grown aerobically. The growth medium for the donor culture also influences these same parameters: a rich medium is superior to a completely synthetic medium. Starvation of donor cells in buffered saline or for a required amino acid results in (i) a loss of F pili, (ii) a loss in the ability of donor-specific phages to adsorb, (iii) a loss of ability to form specific pairs with F(-) cells and to yield recombinants, and (iv) an increase in recipient ability. These changes occur as a function of starvation time, and at rates which are dependent on the conditions of prior growth and starvation of the donor culture. Either treatment provides a rapid method for the production of F(-) phenocopies from donor cultures. Resynthesis of F pili by cells within a starved donor culture commences very soon after restoration of normal growth conditions, but full restoration of donor ability, as measured by recombinant yield, occurs at a slower rate. We found, along with other investigators, that F pili are essential for specific pair formation. We also found, however, that the presence of F pili is not sufficient for display of donor ability, nor is the absence of F pili enough for cells to exhibit recipient ability. This suggests, therefore, that one or more components, in addition to F pili, are necessary for the conversion of specific pairs to effective pairs (or for chromosome mobilization, or both) and for preventing donor cells from acting as recipients. On the basis of our results, we suggest optimal conditions for achieving high mating efficiencies.     

Cloning and characterization of the asd gene of Salmonella typhimurium: use in stable maintenance of recombinant plasmids in Salmonella vaccine strains

The asd mutants of Salmonella typhimurium have an obligate requirement for diaminopimelic acid (DAP) and will undergo lysis in environments deprived of DAP. This has allowed the development of a balanced-lethal system for the expression of heterologous antigens in vaccine strains using vectors containing the wild-type asd gene from Streptococcus mutans and asd mutant Salmonella hosts [Nakayama et al., Biotechnology 6 (1988) 693-697]. We have cloned the asd gene from S. typhimurium, characterized the gene product and used this gene to construct Asd+ expression cloning vectors. In addition we have constructed an asd cassette and a transposon derived from Tn5 that allow the rapid modification of other vectors for use with delta asd vaccine strains of S. typhimurium adding versatility to the Asd+ vector/delta asd host system of plasmid maintenance.     

Binding to Any ESCRT Can Mediate Ubiquitin‐Independent Cargo Sorting

The ESCRT (endosomal sorting complex required for transport) machinery is known to sort ubiquitinated transmembrane proteins into vesicles that bud into the lumen of multivesicular bodies (MVBs). Although the ESCRTs themselves are ubiquitinated they are excluded from the intraluminal vesicles and recycle back to the cytoplasm for further rounds of sorting. To obtain insights into the rules that distinguish ESCRT machinery from cargo we analyzed the trafficking of artificial ESCRT‐like protein fusions. These studies showed that lowering ESCRT‐binding affinity converts a protein from behaving like ESCRT machinery into cargo of the MVB pathway, highlighting the close relationship between machinery and the cargoes they sort. Furthermore, our findings give insights into the targeting of soluble proteins into the MVB pathway and show that binding to any of the ESCRTs can mediate ubiquitin‐independent MVB sorting.     

MyD88 signaling is not essential for induction of antigen-specific B cell responses but is indispensable for protection against Streptococcus pneumoniae infection following oral vaccination with attenuated Salmonella expressing PspA antigen

TLRs directly induce innate host defense responses, but the mechanisms of TLR-mediated adaptive immunity remain subject to debate. In this study, we clarified a role of TLR-mediated innate immunity for induction of adaptive immunity by oral vaccination with a live recombinant attenuated Salmonella enteric serovar Typhimurium vaccine (RASV) strain expressing Streptococcus pneumoniae surface protein A (PspA) Ag. Of note, oral or intranasal vaccination with RASV expressing PspA resulted in identical or even significantly higher levels of PspA-specific IgG and IgA responses in the systemic and mucosal compartments of MyD88(-/-) mice of either BALB/c or C57BL/6 background when compared with those of wild-type mice. Although PspA-specific CD4(+) T cell proliferation in the MyD88(-/-) mice was minimal, depletion of CD4(+) T cells abolished PspA-specific IgG and IgA responses in the MyD88(-/-) mice of BALB/c background. Of the greatest interest, MyD88(-/-) mice that possessed high levels of PspA-specific IgG and IgA responses but minimal levels of CD4(+) T cell responses died earlier than nonvaccinated and vaccinated wild-type mice following i.v. or intranasal challenge with virulent S. pneumoniae. Taken together, these results suggest that innate immunity activated by MyD88 signals might not be necessary for Ag-specific Ab induction in both systemic and mucosal sites but is critical for protection following oral vaccination with attenuated Salmonella expressing PspA.     

A Low Gastric pH Mouse Model to Evaluate Live Attenuated Bacterial Vaccines

The low pH of the stomach serves as a barrier to ingested microbes and must be overcome or bypassed when delivering live bacteria for vaccine or probiotic applications. Typically, the impact of stomach acidity on bacterial survival is evaluated in vitro, as there are no small animal models to evaluate these effects in vivo. To better understand the effect of this low pH barrier to live attenuated Salmonella vaccines, which are often very sensitive to low pH, we investigated the value of the histamine mouse model for this application. A low pH gastric compartment was transiently induced in mice by the injection of histamine. This resulted in a gastric compartment of approximately pH 1.5 that was capable of distinguishing between acid-sensitive and acid-resistant microbes. Survival of enteric microbes during gastric transit in this model directly correlated with their in vitro acid resistance. Because many Salmonella enterica serotype Typhi vaccine strains are sensitive to acid, we have been investigating systems to enhance the acid resistance of these bacteria. Using the histamine mouse model, we demonstrate that the in vivo survival of S. Typhi vaccine strains increased approximately 10-fold when they carried a sugar-inducible arginine decarboxylase system. We conclude that this model will be a useful for evaluating live bacterial preparations prior to clinical trials.