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Many AIDS vaccine candidates under development may elicit immune responses similar to those observed in and used to screen human immunodeficiency virus type 1 (HIV-1)-infected individuals. Therefore, it is important to develop vaccine candidates that incorporate antigenic markers and allow vaccinees to be distinguished from HIV-1 infectees. To this end, we introduced a series of mutations into and in the vicinity of the major immunodominant region (MIR) of gp41 (residues 598–609), a domain recognized by almost all HIV-1 infectees, and evaluated whether HIV-1-like particles incorporating such mutant glycoproteins could be expressed in mammalian cells. Results indicated that although up to three consecutive amino acids could be replaced within MIR without significantly affecting particle formation or gp160 processing, deletions within MIR impaired envelope processing. Replacement of HIV-1 MIR by part or most of the corresponding domain from other lentiviruses markedly decreased or abolished gp160 processing. Synthetic peptides corresponding to a mutated MIR incorporating three amino acid replacements were not recognized by a panel of sera from HIV-1 infectees, suggesting that HIV-1-like particles with this type of mutation represent potential candidate vaccines that could allow vaccinees to be distinguished from HIV-1 infectees.

Aging is associated with a decline in immune function and the elderly are therefore more susceptible to infectious disease and less responsive to vaccination. Influenza antigens complexed as immunostimulatory complexes (ISCOMs) generate more potent protective immune responses compared with non-adjuvanted flu antigens in young adult mice. We report on the protective efficacy of flu-ISCOMs compared with the current split flu vaccine in an aged mouse model. DBA/2 mice aged 2 or 18 months were immunized with flu vaccine, ISCOMs or live virus, prior to challenge with the homologous virus. In aged mice, flu-ISCOMs induced significantly higher serum hemagglutination inhibition (HAI) titers compared to vaccine, similar to the levels obtained in young adult mice that received the split vaccine. Flu-ISCOMs but not vaccine induced cytotoxic T lymphocyte (CTL) responses in young and to a lesser degree in aged mice. In aged mice flu-ISCOMs significantly reduced illness and enhanced recovery from viral infection compared with vaccine. Our data suggests that flu-ISCOMs may offer an improved vaccine strategy for protection of elderly humans against the complications of influenza infection.

A conserved proline residue is found at position 331 in the CH2 domains of human IgG subclasses which fix complement. This residue is replaced by a serine in IgG4 which is inactive. To determine the role of residue 331 in the differential ability of human IgGs to activate the complement cascade, a pair of genetically engineered anti-dinitrophenol IgG1 and IgG4 antibodies with reciprocal mutations at position 331 were tested for their hemolytic activity as well as for their ability to bind C1q, activate C1 and cleave C4. The IgG1 Ser331 mutant was virtually unable to mediate the lysis of trinitrobenzene-sulfonic acid-derivatized sheep red blood cells as a result of a marked defect in C1q binding activity. In contrast, the substitution of Pro for Ser331 in IgG4 bestowed partial hemolytic activity (40%) to the IgG4 Pro331 variant. Under low ionic strength conditions, this mutant was found to be approximately 50 and 75% as active as wild-type IgG1 in the C1q binding and C4b deposition assays, respectively. These results indicate that residue Pro331, which folds into close proximity to a previously identified C1q binding motif (Duncan, A. R., and Winter, G. (1988) Nature 332, 738-740), contributes to the architecture of the IgG1 C1q binding site and that its replacement by a serine residue in IgG4 is largely responsible for the functional inactivity of this isotype.

Although human IgG2 is not cytophilic, we have shown previously that an IgG2 antibody expressing the sequence PLLGG (underline = substitution) spanning CH2 domain residues 233-237 (Eu numbering) displayed IgG1-like Fc gamma RI binding activity. In contrast, IgG1 PLLGG exhibited 3-fold less affinity, whereas IgG2 ELLGG was 3-fold more active than native IgG1. These results suggested that additional site(s) conferred enhanced binding properties to the engineered, cytophilic IgG2 variant. These sites were shown to reside in the IgG2 CH2 domain, since the IgG1 CH2 module did not have enhanced activity in a panel of hybrid IgG1/IgG2 antibodies. To map these sites further, human IgG1 and IgG2 constant region gene segments were modified to allow reciprocal COOH-terminal half segment exchanges of CH2 exons. These were cloned into a pSV2neo expression vector bearing a rearranged MOPC 315 heavy chain variable region gene and transfected into a MOPC 315 heavy chain deletion mutant. The dinitrophenol affinity-purified IgGs were radiolabeled and assessed for Fc gamma RI binding activity in direct binding assays using U937 cells. The COOH terminus of the IgG2 CH2 domain was found to contain accessory site(s) since it enhanced the binding properties of both IgG1 PLLGG and native IgG1. In contrast, grafting of the COOH terminus of the IgG1 CH2 domain onto IgG2 PLLGG and IgG2 ELLGG diminished their cytophilic activity. The amino acid responsible for the enhancing properties of the COOH terminus of the IgG2 CH2 domain was shown to be threonine 339, since IgG1 PLLGG/Thr339 displayed increased Fc gamma RI binding affinity. Kinetics studies revealed that this is accomplished through an increase in the forward rate constant of the IgG-Fc gamma RI interaction.

The genes (dms) encoding the dimethylsulfoxide reductase protein complex have been cloned and sequenced from Haemophilus influenzae (Hi) type b (Hib) strain Eagan. The Hib dms genes are arranged as an operon whose genomic organization is similar to that of the Escherichia coli (Ec) dmsABC operon. The deduced Hib DmsA, and DmsB and DmsC amino-acid sequences are highly homologous to their Ec counterparts and nearly identical to the recently published sequences of the Hi type-d strain Rd Dms proteins. Hi dimethylsulfoxide reductase appears to be a new member of the superfamily of oxidoreductase enzymes.

A human monoclonal IgG1 κ protein (Hom) was found to possess two species of light chain with molecular weights of 23,000 and 28,000 respectively. The difference in mass was due to the presence of a carbohydrate prosthetic group on the 28,000 dalton species. The two species of light chain were separated by chromatography on CM-cellulose. Circular dichroism failed to detect any significant differences in conformation between the glycosylated and non-glycosylated forms and both species recombined with a heavy chain in an identical fashion as judged by difference spectroscopy. An anti-idiotypic antibody raised against the glycosylated Fab-fragment of IgGlHom was unable to distinguish between this species and the non-glycosylated Fab fragment, suggesting that the structure of the combining site is identical or very similar in both molecules. Amino-acid sequence analyses showed that both light chains had an identical sequence up to residue 41. Further studies on the glycosylated light chain, using o -iodosobenzoic acid fragments, localized the carbohydrate attachment site to asparagine 107, the penultimate residue of the J κ region which links V κ to C κ . The sequence around the attachment site was Asn-Arg-Thr which satisfies the requirements for an acceptor sequence. The non-glycosylated light chain was found to have the same sequence in this region indicating that the absence of glycosylation was not due to the lack of an acceptor sequence. A kinetic mechanism has been proposed to account for the incomplete glycosylation of the light chains of IgG1Hom in which there is a competition between the rate of folding of the nascent polypeptide and the rate of attachment of core sugars via the dolichol pyrophosphate pathway.

To identify Fc receptors from human placental microvilli, proteins that were liberated by detergents from human placental synctiotrophoblast microvillous membranes (StMPM) were characterized by their abilities to bind human IgG in immune complexes with sheep or goat anti-human IgG and to monomeric rabbit anti-dinitrophenol (DNP) IgG bound to DNP-lysine Sepharose. Three placental IgG-binding proteins coprecipitated with immune complexes (Mr = 68 000, 52 000–56 000, 40 000) and were designated pIBP68, pIBP56 and pIBP40, respectively. Of the three proteins only pIBP56 bound to immobilized monomeric rabbit IgG. It was isolated from detergent lysates of StMPM and LDS/phenol glycoprotein extracts of placental plasma membranes suggesting that pIBP56 was a glycoprotein FcR previously reported (Mikulska et al, 1982). The binding specificities of pIBP56 and pIBP4o appeared to be detergent dependent. Photoaffinity crosslinking of StMPM surface proteins in situ to monomeric rabbit derivatized with N-succinimidyl(4-azidophenyl)-1,3-dithiopropio-nate identified IgG-binding proteins identical in size to pIBP56 and pIBP4o. Crosslinking further suggested that monomeric IgG covalently bound to a complex of StMPM proteins with a total size of 110000–120000 M, The findings suggest that pIBP68, pIBP56 and pIBP68 are responsible for IgG binding activity of placental StMPM.

We have used a series of sequenced V kappa 21 L-chains produced from murine myelomas to determine whether the V or J segment of the V region is responsible for dictating preferential recombination. In each competitive recombination, equimolar amounts of two different L-chains, selected on the basis of common V or J segments, were allowed to compete for a limiting amount of H-chain. It was found that the J segment of the L-chain was primarily responsible for dictating the ability of a chain to compete and that the nature of residue 96, the first residue of the J segment, was particularly important. Specifically, charged residues caused the L-chain to compete poorly against L-chains with hydrophobic side chains at this position. Furthermore, if Phe or, to a lesser extent, Tyr were present at position 96, the L-chain competed more successfully than chains with Trp-96 or Leu-96. This suggests that both the aromaticity and size of this residue were important factors in determining preferential recombination. It was also found that all other residues in VL were secondary to residue 96 in contributing to the ability of a chain to compete. Finally, unlike all previous studies, we observed a substantial number (64%) of preferred heterologous recombinations. These results are consistent with the hypothesis that the VL and VH gene rearrangements occur independently, thus resulting in random pairing of VH and VL domains.

Competitive reassociation experiments, in which equimolar amounts of two different L-chains were allowed to compete for a limiting amount of H-chain, were performed to assess the role of the V kappa- and J kappa-segments on the ability of an L-chain to compete. Using H- and L-chains from the murine anti-phosphorylcholine (PC) myelomas, TEPC15, MOPC167 and MCPC603, and a series of V kappa 21 L-chains, it was found that the V kappa 21 L-chains competed uniformly better than the anti-PC L-chains, when the anti-PC H-chains were used, despite any differences in the J-segments of the competing L-chains. In addition, when the anti-PC L-chains, which all employ identical J kappa-segments but very diverse V kappa-segments, were in competition against each other, a hierarchy of competitive ability existed which was independent of whether the chains were autologous or heterologous and independent of antigen binding activity. Competitive reassociation experiments between the V kappa 21 and anti-PC L-chains were also performed using the heterologous anti-lysozyme monoclonal HyHEL-10 H-chain or the anti-galactan J539 H-chain, and it was found that the relative competitive ability of the V kappa 21 L-chains with respect to the anti-PC L-chains was dependent on which H-chain was employed. The results suggested that the main factor favouring preferential reassociation by any particular L-chain was the V kappa-segment and that the effects of the J kappa-segment could not be observed where a high degree of diversity in the V-segments existed. Furthermore, while the results implied that specific pairs of VH- and VL-domains had a higher affinity for each other, this was not a necessary criterion in the formation of autologous pairs of H- and L-chains as demonstrated by the preferential heterologous reassociation of the V kappa 21 L-chains over the autologous anti-PC L-chains. These results were consistent with the independent, random rearrangement of immunoglobulin H- and L-chain V-domain gene segments and predict that the hypothetical repertoire of antibodies is not limited by the selection of specific pairs of high-affinity VH-VL domains.