Regulation of T-cell function by antibodies: enhancement of the response of human T-cell clones to hepatitis B surface antigen by antigen-specific monoclonal antibodies

How B cells drive T-cell responses: A key role for cross-presentation of antibody-targeted antigens

In this review we discuss an underexposed mechanism in the adaptive immune system where B cell and T cell immunity collaborate. The main function of B cell immunity is the generation of antibodies which are well known for their high affinity and antigen-specificity. Antibodies can bind antigens in soluble form making so-called immune complexes (ICs) or can opsonize antigen-exposing cells or particles for degradation. This leads to well-known effector mechanisms complement activation, antibody-dependent cytotoxicity and phagocytosis. What is less realized is that antibodies can play an important role in the targeting of antigen to dendritic cells (DCs) and thereby can drive T cell immunity. Here we summarize the studies that described this highly efficient process of antibody-mediated antigen uptake in DCs in vitro and in vivo. Only very low doses of antigen can be captured by circulating antibodies and subsequently trapped by DCs in vivo. We studied the handling of these ICs by DCs in subcellular detail. Upon immune complex engulfment DCs can sustain MHC class I and II antigen presentation for many days. Cell biological analysis showed that this function is causally related to intracellular antigen-storage compartments which are functional endolysosomal organelles present in DCs. We speculate that this function is immunologically very important as DCs require time to migrate from the site of infection to the draining lymph nodes to activate T cells. The implications of these findings and the consequences for the immune system, immunotherapy with tumor-specific antibodies and novel vaccination strategies are discussed.

From therapeutic antibodies to immune complex vaccines

In recent years, therapeutic monoclonal antibodies have made impressive progress, providing great benefit by successfully treating malignant and chronic inflammatory diseases. Monoclonal antibodies with broadly neutralizing effects against specific antigens, or that target specific immune regulators, manifest therapeutic effects via their Fab fragment specificities. Subsequently therapeutic efficacy is mediated mostly by interactions of the Fc fragments of the antibodies with their receptors (FcR) displayed on cells of the immune system. These interactions can trigger a series of immunoregulatory responses, involving both innate and adaptive immune systems and including cross-presentation of antigens, activation of CD₈⁺ T cells and CD₄⁺ T cells, phagocytosis, complement-mediated antibody-dependent cellular cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC). The nature of the triggered effector functions of the antibodies is markedly affected by the glycosylation patterns of the Fc fragments. These can cause differences in the conformation of the heavy chains of antibodies, with resultant changes in antibody binding affinity and activation of the complement system. Studies of the Fc glycosylation profiles together with the associated Fc effector functions and FcR/CR interactions promoted interest and progress in engineering therapeutic antibodies. Furthermore, because antigen–antibody immune complexes (ICs) have shown similar actions, in addition to certain novel immunoregulatory mechanisms that also reshape immune responses, the properties of ICs are being explored in new approaches for prevention and therapy of diseases. In this review, both basic studies and experimental/clinical applications of ICs leading to the development of preventive and therapeutic vaccines are presented.

Immune Complex Vaccination

Antibody/antigen binding results in immune complexes (IC) that have a variety of regulatory functions. One important feature is the enhanced host immune activation against antigen contained in the complex. ICs play important roles at several critical steps that lead to B and T cell activation, including antigen targeting/retention, facilitated antigen uptake, antigen presenting cell activation and proper balancing of positive and negative stimulatory signals. In both poultry industry and clinical health care, ICs have been used as preventive and therapeutic vaccines. With our deepening understanding of antibody biology, particularly in light of new revelations of regulatory functions of Fc receptors, mechanistically more precise engineering has spearheaded tailored use of this tool for infection control and cancer therapy. IC-based treatment and prophylaxis have been tested to different extents in HBV, HIV and influenza viral infection control and are actively examined as an alternative treatment for several forms of tumor. As a part of this book series, this chapter aims to discuss the mechanistic aspects of IC signaling and their impact on immune cells. We give samples how this old technology has been used by practitioners over the last several decades and suggest potential paths for future development of IC-based immune therapy.

Effects of Bovine Immunoglobulins on Immune Function, Allergy, and Infection

This review aims to provide an in depth overview of the current knowledge of the effects of bovine immunoglobulins on the human immune system. The stability and functional effects of orally ingested bovine immunoglobulins in milk products are described and potential mechanisms of action are discussed. Orally ingested bovine IgG (bovine IgG) can be recovered from feces, ranging from very low levels up to 50% of the ingested IgG that has passed through the gastrointestinal tract. In infants the recovered levels are higher than in adults most likely due to differences in stomach and intestinal conditions such as pH. This indicates that bovine IgG can be functionally active throughout the gastrointestinal tract. Indeed, a large number of studies in infants and adults have shown that bovine IgG (or colostrum as a rich source thereof) can prevent gastrointestinal tract infections, upper respiratory tract infections, and LPS-induced inflammation. These studies vary considerably in target group, design, source of bovine IgG, dosage, and endpoints measured making it hard to draw general conclusions on effectiveness of bovine immunoglobulin rich preparations. Typical sources of bovine IgG used in human studies are serum-derived IgG, colostrum, colostrum-derived IgG, or milk-derived immunoglobulins. In addition, many studies have used IgG from vaccinated cows, but studies using IgG from nonimmunized animals have also been reported to be effective. Mechanistically, bovine IgG binds to many human pathogens and allergens, can neutralize experimental infection of human cells, and limits gastrointestinal inflammation. Furthermore, bovine IgG binds to human Fc receptors which, enhances phagocytosis, killing of bacteria and antigen presentation and bovine IgG supports gastrointestinal barrier function in in vitro models. These mechanisms are becoming more and more established and explain why bovine IgG can have immunological effects in vivo. The inclusion of oral bovine immunoglobulins in specialized dairy products and infant nutrition may therefore be a promising approach to support immune function in vulnerable groups such as infants, children, elderly and immunocompromised patients.

Immunoregulatory functions of immune complexes in vaccine and therapy

Clinical and experimental preparations of IgG/soluble antigen complexes, as well as those formed following antibody therapy in vivo, are multifaceted immune regulators. These immune complexes (ICs) have been tested in humans and animal models, mostly in forms of experimental or clinical vaccination, for at least a century. With intensified research on Fcγ receptor-mediated immune modulation, as well as with immune complex-directed antigen processing, presentation, and inflammatory responses, there are renewed interests of using ICs in vaccines and immunotherapies. Currently, IC-based immune therapy has been broadly experimented in HBV and HIV viral infection control and antitumor treatments. However, mechanistic insights of IC-based treatments are relatively recent subjects of study; strong efforts are needed to establish links to connect laboratory findings with clinical practices. This review covers the history, mechanisms, and in vivo outcomes of this safe and effective therapeutic tool, with a clear aim to bridge laboratory findings with evolving clinical applications.

Understanding MHC class I presentation of viral antigens by human dendritic cells as a basis for rational design of therapeutic vaccines

Effective viral clearance requires the induction of virus-specific CD8⁺ cytotoxic T lymphocytes (CTL). Since dendritic cells (DC) have a central role in initiating and shaping virus-specific CTL responses, it is important to understand how DC initiate virus-specific CTL responses. Some viruses can directly infect DC, which theoretically allow direct presentation of viral antigens to CTL, but many viruses target other cells than DC and thus the host depends on the cross-presentation of viral antigens by DC to activate virus-specific CTL.

Research in mouse models has highly enhanced our understanding of the mechanisms underlying cross-presentation and the dendritic cells (DC) subsets involved, however, these results cannot be readily translated toward the role of human DC in MHC class I-antigen presentation of human viruses. Here, we summarize the insights gained in the past 20 years on MHC class I presentation of viral antigen by human DC and add to the current debate on the capacities of different human DC subsets herein. Furthermore, possible sources of viral antigens and essential DC characteristics for effective induction of virus-specific CTL are evaluated.

We conclude that cross-presentation is not only an efficient mechanism exploited by DC to initiate immunity to viruses that do not infect DC but also to viruses that do infect DC, because cross-presentation has many conceptual advantages and bypasses direct immune modulatory effects of the virus on its infected target cells.

Since knowledge on the mechanism of viral antigen presentation and the preferred DC subsets is crucial for rational vaccine design, the obtained insights are very instrumental for the development of effective anti-viral immunotherapy.

Antigen cross-presentation of immune complexes

The ability of dendritic cells (DCs) to cross-present tumor antigens has long been a focus of interest to physicians, as well as basic scientists, that aim to establish efficient cell-based cancer immune therapy. A prerequisite for exploiting this pathway for therapeutic purposes is a better understanding of the mechanisms that underlie the induction of tumor-specific cytotoxic T-lymphocyte (CTL) responses when initiated by DCs via cross-presentation. The ability of humans DC to perform cross-presentation is of utmost interest, as this cell type is a main target for cell-based immunotherapy in humans. The outcome of a cross-presentation event is guided by the nature of the antigen, the form of antigen uptake, and the subpopulation of DCs that performs presentation. Generally, CD8α⁺ DCs are considered to be the most potent cross-presenting DCs. This paradigm, however, only applies to soluble antigens. During adaptive immune responses, immune complexes form when antibodies interact with their specific epitopes on soluble antigens. Immunoglobulin G (IgG) immune complexes target Fc-gamma receptors on DCs to shuttle exogenous antigens efficiently into the cross-presentation pathway. This receptor-mediated cross-presentation pathway is a well-described route for the induction of strong CD8⁺ T cell responses. IgG-mediated cross-presentation is intriguing because it permits the CD8⁻ DCs, which are commonly considered to be weak cross-presenters, to efficiently cross-present. Engaging multiple DC subtypes for cross-presentation might be a superior strategy to boost CTL responses in vivo. We here summarize our current understanding of how DCs use IgG-complexed antigens for the efficient induction of CTL responses. Because of its importance for human cell therapy, we also review the recent advances in the characterization of cross-presentation properties of human DC subsets.

Vaccine therapies for chronic hepatitis B: can we go further?

Chronic hepatitis B is a major health burden worldwide. In addition to the recent progress in antiviral treatment, therapeutic vaccination is a promising new strategy for the control of chronic hepatitis B. On the basis of the major specific and non-specific immune dysregulations and defects in chronic hepatitis B patients, this paper presents the peptide and protein-based, DNA-based, cell-based, and antigen-antibody-based therapeutic vaccines, which have undergone clinical trials. The advantages, disadvantages, and future perspectives for these therapeutic vaccines are discussed.

Immune-complex mimics as a molecular platform for adjuvant-free vaccine delivery

Protein-based vaccine development faces the difficult challenge of finding robust yet non-toxic adjuvants suitable for humans. Here, using a molecular engineering approach, we have developed a molecular platform for generating self-adjuvanting immunogens that do not depend on exogenous adjuvants for induction of immune responses. These are based on the concept of Immune Complex Mimics (ICM), structures that are formed between an oligomeric antigen and a monoclonal antibody (mAb) to that antigen. In this way, the roles of antigens and antibodies within the structure of immune complexes are reversed, so that a single monoclonal antibody, rather than polyclonal sera or expensive mAb cocktails can be used. We tested this approach in the context of Mycobacterium tuberculosis (MTB) infection by linking the highly immunogenic and potentially protective Ag85B with the oligomeric Acr (alpha crystallin, HspX) antigen. When combined with an anti-Acr monoclonal antibody, the fusion protein formed ICM which bound to C1q component of the complement system and were readily taken up by antigen-presenting cells in vitro. ICM induced a strong Th1/Th2 mixed type antibody response, which was comparable to cholera toxin adjuvanted antigen, but only moderate levels of T cell proliferation and IFN-γ secretion. Unfortunately, the systemic administration of ICM did not confer statistically significant protection against intranasal MTB challenge, although a small BCG-boosting effect was observed. We conclude that ICM are capable of inducing strong humoral responses to incorporated antigens and may be a suitable vaccination approach for pathogens other than MTB, where antibody-based immunity may play a more protective role.

B Cell in Autoimmune Diseases

The role of B cells in autoimmune diseases involves different cellular functions, including the well-established secretion of autoantibodies, autoantigen presentation and ensuing reciprocal interactions with T cells, secretion of inflammatory cytokines, and the generation of ectopic germinal centers. Through these mechanisms B cells are involved both in autoimmune diseases that are traditionally viewed as antibody mediated and also in autoimmune diseases that are commonly classified as T cell mediated. This new understanding of the role of B cells opened up novel therapeutic options for the treatment of autoimmune diseases. This paper includes an overview of the different functions of B cells in autoimmunity; the involvement of B cells in systemic lupus erythematosus, rheumatoid arthritis, and type 1 diabetes; and current B-cell-based therapeutic treatments. We conclude with a discussion of novel therapies aimed at the selective targeting of pathogenic B cells.

Fc receptor-targeted mucosal vaccination as a novel strategy for the generation of enhanced immunity against mucosal and non-mucosal pathogens

Numerous studies have demonstrated that targeting immunogens to Fcgamma receptors (FcgammaR) on antigen (Ag)-presenting cells (APC) can enhance humoral and cellular immunity in vitro and in vivo. FcgammaR are classified based on their molecular weight, IgG-Fc binding affinities, IgG subclass binding specificity, and cellular distribution and they consist of activating and inhibitory receptors. However, despite the potential advantages of targeting Ag to FcR at mucosal sites, very little is known regarding the role of FcR in mucosal immunity or the efficacy of FcR-targeted mucosal vaccines. In addition, recent work has suggested that FcRn is present in the lungs of adult mice and humans and can transport FcRn-targeted Ag to FcgammaR-bearing APC within mucosal lymphoid tissue. In this review we will discuss the need for new vaccine strategies, the potential for FcR-targeted vaccines to fill this need, the impact of activating versus inhibitory FcgammaR on FcR-targeted vaccination, the significance of focusing on mucosal immunity, as well as caveats that could impact the use of FcR targeting as a mucosal vaccine strategy.

Utilization of Fc receptors as a mucosal vaccine strategy against an intracellular bacterium, Francisella tularensis

Numerous studies have demonstrated that targeting Ag to Fc receptors (FcR) on APCs can enhance humoral and cellular immunity. However, studies are lacking that examine both the use of FcR-targeting in generating immune protection against infectious agents and the use of FcRs in the induction of mucosal immunity. Francisella tularensis is a category A intracellular mucosal pathogen. Thus, intense efforts are underway to develop a vaccine against this organism. We hypothesized that protection against mucosal infection with F. tularensis would be significantly enhanced by targeting inactivated F. tularensis live vaccine strain (iFt) to FcRs at mucosal sites, via intranasal immunization with mAb-iFt complexes. These studies demonstrate for the first time that: 1) FcR-targeted immunogen enhances immunogen-specific IgA production and protection against subsequent infection in an IgA-dependent manner, 2) FcgammaR and neonatal FcR are crucial to this protection, and 3) inactivated F. tularensis, when targeted to FcRs, enhances protection against the highly virulent SchuS4 strain of F. tularensis, a category A biothreat agent. In summary, these studies show for the first time the use of FcRs as a highly effective vaccination strategy against a highly virulent mucosal intracellular pathogen.

Vaccination with recombinant HBsAg-HBIG complex in healthy adults

A therapeutic vaccine for viral hepatitis B composed of yeast-derived recombinant HBsAg complexed to human anti-HBs immunoglobulin (yeast-derived-immunogenic complex, YIC) with alum as the adjuvant was evaluated for safety. In stage 1, 22 healthy Chinese adult volunteers were vaccinated with three doses of 30 microg, 60 microg or 90 microg of HBsAg in YIC at 4-week intervals. In stage 2, nine volunteers received 90 microg of HBsAg in YIC for six injections. All immunizations were well tolerated. Renal, liver function and other blood chemistry tests remained within normal range. All recipients developed serum anti-HBs, the highest being 1000 mIU/ml, and the subtypes of anti-HBs were IgG1 and IgG3. The serum levels of interferon-gamma (IFN-gamma) and interleukin-2 (IL-2) were increased, while no significant increase was observed in interleukin-4 (IL-4), interleukin-6 (IL-6), interleukin-10 (IL-10) or tumor necrosis factor-alpha (TNF-alpha). These results indicate that this complex is safe and can induce a potent anti-HBs response.

Protective levels of polysaccharide-specific maternal antibodies may enhance the immune response elicited by pneumococcal conjugates in neonatal and infant mice

Maternal antibodies (MatAbs) may protect the offspring against infections but may also interfere with their immune responses to vaccination. We have previously shown that maternal immunization with pneumococcal polysaccharides (PPS) conjugated to tetanus protein (Pnc-TT) protected the offspring against infections caused by three important pediatric serotypes. To study the influence of MatAb on the immune response to Pnc-TT early in life, adult female mice were immunized twice with Pnc-TT of serotype 1 (Pnc1-TT), and their offspring received Pnc1-TT subcutaneously three times at 3-week intervals starting at 1 week (neonatal) or 3 weeks (infant) of age. High levels of PPS-1-specific MatAb (>3 log) in offspring of Pnc1-TT-immunized dams completely inhibited their anti-PPS-1 response elicited by Pnc1-TT. In contrast, low or moderate ( approximately 1 to 2 log) levels of MatAb did not interfere with and even enhanced the immune response of the offspring, and a booster response to a second Pnc1-TT dose was observed. Carrier-specific MatAbs had little effect on the response of offspring to the conjugate. All Pnc1-TT-immunized offspring were protected against pneumococcal bacteremia and had reduced lung infection. These results demonstrate that in the presence of MatAb, Pnc1-TT may elicit a protective PPS-1-specific antibody response and prime for PPS-1-specific memory in young offspring. Importantly, low or moderate levels of PPS-1-specific MatAb not only provided protection against pneumococcal infections but also enhanced the immune response elicited by Pnc1-TT in neonatal and infant mice. This murine model will be used to develop novel strategies combining maternal and neonatal immunization to protect against infections caused by encapsulated bacteria in early life.

Lack of effective T-lymphocyte response to the PAX3/FKHR translocation area in alveolar rhabdomyosarcoma

PURPOSE

Alveolar rhabdomyosarcoma (ARMS) frequently contains the fusion transcription factor PAX3/FKHR. Therefore, clinical studies have been initiated to utilize the PAX3/FKHR translocation point area as a peptide vaccine against ARMS. Our study was directed at identifying antigenic T-lymphocyte epitopes at the PAX3/FKHR translocation point area.

EXPERIMENTAL DESIGN

The peptide sequence surrounding the PAX3/FKHR translocation point was evaluated by MHC binding algorithms for potential T-lymphocyte antigenic epitopes (class I molecules HLA-A1, -A2 and -A3; class II molecules HLA-DR1, -DR4 and -DR7). Using in vitro techniques, dendritic cells loaded with PAX3/FKHR peptides were used to stimulate naive T-lymphocytes. T-lymphocyte activity was then evaluated by 51Cr release and 3H-thymidine uptake assays.

RESULTS

Only one HLA-A3-restricted epitope was predicted by the algorithms. The peptide was prepared and tested for its ability to stimulate naive cytotoxic T-lymphocytes (CTLs). Unfortunately, the peptide was unsuccessful at stimulating naive CTL. However, induction of naive helper T-lymphocytes (HTL) to recognize and respond to the PAX3/FKHR translocation peptide was successful. Yet, this HTL peptide activity did not translate into recognition of PAX3/FKHR-containing ARMS tumor cells.

CONCLUSIONS

It appears that the fusion area of PAX3/FKHR may not be a good source of antigenic anti-tumor peptide epitopes. These results raise serious concerns about the success and applicability of future peptide-based vaccine immunotherapy directed at the PAX3/FKHR translocation point.

Influence of maternal antibodies on neonatal immunization against respiratory viruses

Vaccines that successfully prevent severe infant respiratory virus diseases should induce protection at a very young age because of the low age of patients who are hospitalized owing to these viruses. Candidate respiratory virus vaccines are being tested in infants who are naïve to infection but seropositive to the viral agents because they possess maternal IgG antibodies (Abs). Transplacental maternal Abs may be partially protective against disease caused by respiratory virus infections. Carefully conducted studies have shown that these Abs can also profoundly suppress or enhance infant immune responses to immunization. The mechanisms underlying regulation of immune responses to viruses by maternal Abs are under investigation. This article explores the current knowledge regarding the effect of maternal Abs on respiratory virus and measles virus immunization, and it reviews the current approaches to overcoming Ab-mediated immunosuppression.

Multiple roles for the major histocompatibility complex class I- related receptor FcRn

Multiple functions have recently been identified for the neonatal Fc receptor FcRn. In addition, a human homolog of the rodent forms of FcRn has been identified and characterized. This major histocompatibility complex class I-related receptor plays a role in the passive delivery of immunoglobulin (Ig)Gs from mother to young and the regulation of serum IgG levels. In addition, FcRn expression in tissues such as liver, mammary gland, and adult intestine suggests that it may modulate IgG transport at these sites. These diverse functions are apparently brought about by the ability of FcRn to bind IgGs and transport them within and across cells. However, the molecular details as to how FcRn traffics within cells have yet to be fully understood, although in vitro systems have been developed for this purpose. The molecular nature of the FcRn-IgG interaction has been studied extensively and encompasses residues located at the CH2-CH3 domain interface of the Fc region of IgG. These Fc amino acids are highly conserved in rodents and man and interact with residues primarily located on the alpha2 domain of FcRn. Thus, it is now possible to engineer IgGs with altered affinities for FcRn, and this has relevance to the modulation of IgG serum half-life and maternofetal IgG transport for therapeutic applications.

Get into the groove! Targeting antigens to MHC class II

The activation of MHC class II-restricted helper T cells is paramount to adaptive immune responses. Vaccine development could therefore benefit from improved ways of targeting antigens into MHC class II molecules. In recent years, the natural pathways of MHC class II antigen presentation have been exploited to achieve this goal. First, antigenic proteins and peptides have been modified to facilitate receptor-mediated uptake by professional antigen-presenting cells. Second, DNA constructs containing specific targeting sequences have been used to direct endogenously synthesized antigens to the MHC class II compartments. Both strategies proved to be highly effective. We review these data and describe how this knowledge is currently applied to the design of vaccines that activate helper T cells in vivo.

The role of B cells in the establishment of T cell response in mice infected with an intracellular bacteria, Listeria monocytogenes

To clarify the role of B cells in the establishment of T cell response against intracellular bacteria, B-cell-deficient (muMT-/-) mice were infected with an intracellular bacteria, Listeria monocytogenes, and T cell response against the bacteria was analyzed. On day 6 of primary Listeria infection, spleen T cells of the muMT-/- mice showed significantly lower levels of proliferative response and IFN-gamma production than those of normal infected mice after in vitro stimulation with listerial antigen. Even in the secondary Listeria infection after immunization with viable bacteria, spleen T cells of the muMT-/- mice proliferated and produced IFN-gamma against listerial antigen at significantly lower levels than those of normal immunized mice. These results demonstrate participation of B cells in priming of Listeria-specific T cells in vivo. However, B cells failed to present Listeria antigen to Listeria-specific T cells in vitro unless Listeria antigen was solubilized. Furthermore, transfer of immune serum from Listeria-infected normal mice failed to enhance the Listeria-specific T cell response of muMT-/- mice. The results indicate that B cells support the T cell response against intracellular bacteria through a mechanism other than their Ig production or antigen presentation function.

Presentation of antigen in immune complexes is boosted by soluble bacterial immunoglobulin binding proteins

Using a snake toxin as a proteic antigen (Ag), two murine toxin-specific monoclonal antibodies (mAbs), splenocytes, and two murine Ag-specific T cell hybridomas, we showed that soluble protein A (SpA) from Staphylococcus aureus and protein G from Streptococcus subspecies, two Ig binding proteins (IBPs), not only abolish the capacity of the mAbs to decrease Ag presentation but also increase Ag presentation 20-100-fold. Five lines of evidence suggest that this phenomenon results from binding of an IBP-Ab-Ag complex to B cells possessing IBP receptors. First, we showed that SpA is likely to boost presentation of a free mAb, suggesting that the IBP-boosted presentation of an Ag in an immune complex results from the binding of IBP to the mAb. Second, FACS analyses showed that an Ag-Ab complex is preferentially targeted by SpA to a subpopulation of splenocytes mainly composed of B cells. Third, SpA-dependent boosted presentation of an Ag-Ab complex is further enhanced when splenocytes are enriched in cells containing SpA receptors. Fourth, the boosting effect largely diminishes when splenocytes are depleted of cells containing SpA receptors. Fifth, the boosting effect occurs only when IBP simultaneously contains a Fab and an Fc binding site. Altogether, our data suggest that soluble IBPs can bridge immune complexes to APCs containing IBP receptors, raising the possibility that during an infection process by bacteria secreting these IBPs, Ag-specific T cells may activate IBP receptor-containing B cells by a mechanism of intermolecular help, thus leading to a nonspecific immune response.

Immunization against hepatitis B virus by mucosal administration of antigen-antibody complexes

Antigen-antibody complexes have been shown to enhance immune responses against several antigens given by parenteral immunization. Herein, we have evaluated the potential of administering such immunostimulatory complexes by a mucosal route. Hepatitis B surface antigen (HBsAg) complexed with antibodies against HBsAg (anti-HBs) (HBsAg/Ab) was administered to BALB/c mice by intranasal inhalation. HBsAg by itself did not induce immune responses, whereas with HBsAg/Ab complexes, both systemic and mucosal immune responses were observed and these could be modulated by adjuvants. With HBsAg/Ab (1 or 10 microg), anti-HBs antibodies induced were predominantly of the IgG1 isotype (Th2-like). In contrast, anti-HBs induced by HBsAg/Ab plus cholera toxin (CT) or oligodeoxynucleotides (ODN) containing immunostimulatory CpG motifs (CpG) (1 microg each) were predominantly IgG2a (Th1-like). Results from this study indicate that HBsAg/Ab complexes can induce strong humoral immune responses when delivered by a noninvasive route, whether used alone or in combination with other mucosal adjuvants.

The serum albumin-binding region of streptococcal protein G (BB) potentiates the immunogenicity of the G130-230 RSV-A protein

BBG2Na is a protein comprising residues 130-230 of the respiratory syncytial virus subgroup A (RSV-A) G protein (G2Na) fused to the albumin-binding domain of streptococcal G protein (BB). BBG2Na was cloned, expressed in Escherichia coli and renaturated. In rodent models, this subunit RSV vaccine adjuvanted in Alhydrogel induced specific antibodies and conferred protection to RSV infection. Comparison of the antibody production in a BALB/c mouse model revealed that BBG2Na induced a stronger and earlier G2Na antibody response than G2Na alone, without altering the IgG subclass distribution. To address the role of the BB part, we explored its carrier properties and showed that it is a Th dependent antigen, generating a more potent G2Na-specific B cell memory response and able to generate Th cells that provide help for G2Na antibody production.

Influence of maternal antibodies on vaccine responses: inhibition of antibody but not T cell responses allows successful early prime-boost strategies in mice

The transfer of maternal antibodies to the offspring and their inhibitory effects on active infant immunization is an important factor hampering the use of certain vaccines, such as measles or respiratory syncytial virus vaccine, in early infancy. The resulting delay in protection by conventional or novel vaccines may have significant public health consequences. To define immunization approaches which may circumvent this phenomenon, experiments were set up to further elucidate its immunological bases. The influence of maternal antibodies on antibody and T cell responses to measles hemagglutinin (MV-HA) were analyzed following MV-HA immunization of pups born to immune or control BALB/c mothers using four different antigen delivery systems: live or inactivated conventional measles vaccine, a live recombinant canarypox vector and a DNA vaccine. High levels (> 5 log10) of maternal anti-HA antibodies totally inhibited antibody responses to each of the vaccine constructs, whereas normal antibody responses were elicited in presence of lower titers of maternal antibodies. However, even high titers of maternal antibodies affected neither the induction of vaccine-specific Th1/Th2 responses, as assessed by proliferation and levels of IFN-gamma and IL-5 production, nor CTL responses in infant mice. On the basis of these unaltered T cell responses, very early priming and boosting (at 1 and 3 weeks of age, respectively) with live measles vaccine allowed to circumvent maternal antibody inhibition of antibody responses in pups of immune mothers. This was confirmed in another immunization model (tetanus toxoid). It suggests that effective vaccine responses may be obtained earlier in presence of maternal antibodies through the use of appropriate immunization strategies using conventional or novel vaccines for early priming.

Effect of plasmid DNA on immunogenicity of HBsAg-anti-HBs complex

Hepatitis B surface antigen (HBsAg) complexed with anti-HBs is more immunogenic than HBsAg alone in mice. This complex is usually used with alum as an adjuvant, which can enhance humoral response but inhibits cell-mediated immune responses. To improve the immunogenicity of HBsAg-anti-HBs, we immunized mice with a combination of this immunogenic complex and pCMVHBs, a plasmid encoding HBsAg, or the vector pCMV. Both plasmids enhanced the anti-HBs response induced by the immunogenic complex. We found 20 microg of plasmid or vector enhanced the anti-HBs response in all mice, whereas 1 microg was less effective. Splenocytes from different immunized groups were stimulated with HBsAg in vitro, and the highest level of IL-2 detected in the supernatant was found in mice immunized with HBsAg-anti-HBs plus pCMVHBs. A plasmid (pcDNA3c191) encoding core protein of hepatitis C virus (HCV) was used as an adjuvant to the immunogenic complex. A preliminary result showed that pcDNA3c191 not only enhanced the immunogenicity of HBsAg-anti-HBs, but also induced anti-HCV core antibodies. Immunization using a plasmid DNA encoding one viral antigen in combination with antigen and antibody complex of another microbial origin could be a new approach to the development of multivalent vaccines.

Determinant spreading: lessons from animal models and human disease

Spreading of the immune response is a common theme in organ-specific and systemic autoimmune diseases. We evaluated whether some of the mixed antinuclear antibody patterns characteristic of systemic autoimmunity might be the result of determinant spreading from a single initiating event. Immunisation of healthy mice with individual protein components of the La/Ro ribonucleoprotein (RNP) targeted in systemic lupus erythematosus and primary Sjögren's syndrome induced autoantibodies recognising Ro60 (SS-A), Ro52 (SS-A) and La (SS-B) and in some cases the molecular chaperones calreticulin and Grp78. The endogenous antigen(s) driving determinant spreading might be derived from physiological apoptosis which could explain the involvement of some chaperone proteins in the autoimmune response. Diversified anti-La/Ro antibody responses were initiated by challenge with a single subdominant T epitope of La even though some self epitopes of La were efficiently tolerised. The pattern of autoantibody responses in primary Sjögren's syndrome was strongly influenced by HLA class II phenotype which we speculate controls activation of T cells recognising defined peptides from the La/Ro RNP. In this way, HLA class II alleles may be critical in influencing initiation and spreading of systemic autoimmune reactions. Molecular mimicry of such determinants by exogenous agents might readily initiate spreading of an autoimmune response in genetically susceptible hosts.

DNA-mediated immunization in a transgenic mouse model of the hepatitis B surface antigen chronic carrier state

Transgenic mice expressing the sequences coding for the envelope proteins of the hepatitis B virus (HBV) in the liver have been used as a model of the HBV chronic carrier state. We evaluated the possibility of inducing a specific immune response to the viral envelope antigens and thus potentially controlling chronic HBV infection. Using HBV-specific DNA-mediated immunization in this transgenic model, we show that the immune response induced after a single intramuscular injection of DNA resulted in the complete clearance of circulating hepatitis B surface antigen and in the long-term control of transgene expression in hepatocytes. This response does not involve a detectable cytopathic effect in the liver. Adoptive transfer of fractionated primed spleen cells from DNA-immunized mice shows that T cells are responsible for the down-regulation of HBV mRNA in the liver of transgenic mice. To our knowledge, this is the first demonstration of a potential immunotherapeutic application of DNA-mediated immunization against an infectious disease and raises the possibility of designing more effective ways of treating HBV chronic carriers.

Relationship between facilitated allergen presentation and the presence of allergen-specific IgE in serum of atopic patients

Allergen presentation to allergen-specific T cells can be facilitated when IgE-allergen complexes are endocytosed by antigen-presenting cells (APC) after binding to the low-affinity Fc epsilon R type II (CD23). Here we present a study on the relative capabilities of sera of atopic patients to mediate facilitated antigen presentation (FAP). To this aim FAP was studied in an in vitro model in which CD23-expressing Epstein-Barr virus (EBV)-B cells act as APC to T lymphocyte clones (TLC) that are specific for Der p 2, a major allergen of housedust mite Dermatophagoides pteronyssinus (Dp). Der p 2 is immune-complexed by preincubation in sera from atopic patients, containing allergen-specific IgE. If EBV-B cells are preincubated with these complexes before using the cells as APC, the allergen-specific TLC proliferate at 100-1000-fold lower allergen concentration than required for T cell activation after presentation of uncomplexed allergen. The relative capability of various sera to mediate FAP was correlated with total serum IgE, and especially with Der p 2-specific serum IgE. In the model used, a high FAP capacity could be demonstrated only in sera with a total serum IgE concentration above approximately 2 micrograms/ml or with Der p 2-specific IgE above approximately 100 ng/ml. Maximal FAP, i.e. the ability to induce maximal proliferation of the TLC, was obtained in the presence of more than +/- 600 ng Der p 2-specific IgE/ml. At 100-600 ng/ml Der p 2-specific IgE the level of FAP was correlated with the concentration of allergen-specific IgE, whereas at lower concentrations FAP was low or absent. All tested sera from eczema patients, all having serum anti-Der p 2-IgE concentrations > 600 ng/ml, showed a high FAP capacity, whereas all tested sera from atopic patients without eczema, which had serum anti-Der p 2-IgE levels < 600 ng/ml, showed no or a low FAP capacity. The association of high FAP capacity with eczema may reflect a functional role of FAP in the pathogenesis of atopic dermatitis.

Intra- and intermolecular spreading of autoimmunity involving the nuclear self-antigens La (SS-B) and Ro (SS-A)

We have tested the extent of immune self-tolerance to the ubiquitously expressed nuclear/cytoplasmic autoantigens La (SS-B) and Ro (SS-A) in healthy, nonautoimmune mice. Immunization of mice with recombinant mouse La resulted in a specific, isotype-switched autoantibody response, which was initially directed toward the La C subfragment (aa 111-242) but rapidly spread to involve the La A (aa 1-107) and La F (aa 243-345) regions of the La antigen. Intramolecular spreading of the anti-La antibody response was further demonstrated by the appearance of autoantibodies to multiple, nonoverlapping antigenic regions of La, after immunization of mice with the 107-aa La A subfragment. Moreover, immunization of mice with recombinant mouse or human La also elicited specific anti-60-kDa Ro IgG antibodies in all strains tested. Mice immunized with 60-kDa Ro produced a high titer anti-Ro antibody response, which was also associated with intermolecular spreading, resulting in the specific appearance of anti-La autoantibodies. These findings show that the development of autoantibodies to multiple components of the La/Ro ribonucleoprotein complex may follow initiation of immunity to a single component. In addition, the data reveal the incomplete nature of immune tolerance to La and Ro despite their endogenous expression in all nucleated cells. These observations are likely to account for the coexistence of anti-La/Ro antibodies in autoimmune disease and suggest a general explanation for the appearance of mixed autoantibody patterns in systemic autoimmune disorders.

B-T lymphocyte interactions in experimental autoimmune myasthenia gravis: autoantibody mediated up-regulation of the response of acetylcholine receptor-specific T lymphocytes

Twenty-six monoclonal antibodies of five different isotypes and reactive against distinct parts (alpha, beta, gamma, delta-subunits) of the nicotinic acetylcholine receptor (AChR) from Torpedo californica were screened for their capacity to enhance activation of AChR-specific CD4+ autoreactive T cells. The T-cell line (LR) used in this study recognized an epitope (98-116) on the alpha-subunit of Torpedo AChR. Four monoclonal antibodies bearing a gamma 2b isotype and recognizing an epitope on the Torpedo AChR alpha-subunit, especially the main immunogenic region (MIR), were able to enhance T-cell activation in a dose-response manner. Four further gamma 2b isotype monoclonal antibodies, recognizing epitopes other than the AChR alpha-subunit, had no effect. Monoclonal antibodies of other isotypes (IgM, IgG1, IgG2a, IgG2c), irrespective of their subunit specificity, were unable to influence the T-cell response. Thus, the enhancement requires a IgG2b isotype, and both the antibody and the T-cell recognize an epitope on the same subunit. We have previously shown that AChR-specific B cells are directly able to present antigen to AChR-specific T-cell lines in a privileged way. The present data demonstrate that B cells are also capable of enhancing indirectly the immunogenicity of autoantigens via their humoral antibodies.

Genesis of host IgE competence: perinatal IgE tolerance induced by IgE processed and presented by IgE Fc receptor (CD23)-bearing B cells

A murine model for studying life-long IgE tolerance was previously developed in this laboratory by perinatal IgE injection into neonates. Herein, we demonstrated that normal and immortal CD23+ B cell lines presented processed IgE via CD23-mediated endocytic pathway and triggered perinatal IgE tolerance. The observations were as followed: (a) CD23 on normal B cells or B cell hybridomas mediated IgE-dependent perinatal IgE tolerance and total IgE deficiency; and lack of either antigen-specific IgE or total IgE did not correlate with elevated levels of autologous anti-IgE in individual mice; (b) IgE tolerance-inducing capacity of CD23+ B cell hybridomas was augmented by treatment with antigen-IgE complexes or interleukin 4, and significantly inhibited by anti-CD23 prior to IgE pulsing; (c) antigen-IgE complexes were endocytosed and degraded in acid hydrolases-containing vesicles; and IgE tolerance was abrogated by treating IgE-pulsed 17A11 at 4 degrees C or 20 degrees C followed immediately by fixation, and by treating IgE-pulsed 17A11 with metabolic inhibitors that elevated intracellular pH of the endocytic vesicles. In conclusion, this study suggested that one pivotal step of genetic control of IgE responses may be exercised at the early developmental stage of T cells of the IgE lineage, and that CD23 may facilitate capture of endogenously secreted IgE, and mediate endocytic processing and presentation of self IgE epitope(s), and thus contribute to the genesis of host IgE competence.

The cellular basis for lack of antibody response to hepatitis B vaccine in humans

We had previously obtained evidence that among normal subjects the humoral antibody response to hepatitis B surface antigen (HBsAg) was bimodally distributed with about 14% of subjects producing less than 1,000 estimated radioimmunoassay RIA units. From the study of major histocompatibility complex (MHC) markers in the very poor responders who produced less than 36 estimated RIA units of antibody, it appeared that there was an excess of homozygotes for two extended haplotypes [HLA-B8, SC01, DR3] and [HLA-B44, FC31, DR7]. This finding suggested that a poor response was inherited as a recessive trait requiring nonresponse genes for HBsAg on both MHC haplotypes and was strengthened by finding a much lower antibody response among prospectively immunized homozygotes for [HLA-B8, SC01, DR3] compared with heterozygotes. In the present study, we have analyzed the cellular basis for nonresponse to this antigen by examining antigen-specific proliferation of T cells from responders and nonresponders in the presence and absence of autologous CD8+ (suppressor) cells. Peripheral blood cells from nonresponders to HBsAg failed to undergo a proliferative response to recombinant HBsAg in vitro, whereas cells from responders proliferated vigorously. This failure of cells from nonresponders to proliferate was not reversed in cell mixtures containing CD4+ and antigen-presenting cells devoid of CD8+ cells. There was no difference between responders and nonresponders with respect to the number of circulating T cells or their subsets, or the proliferative response to mitogens such as pokeweed or phytohemagglutinin or another antigen, tetanus toxoid. Our results indicate that our HBsAg nonresponding subjects have a very specific failure in antigen presentation or the stimulation of T helper cells, or both. Our evidence is against specific immune suppression as the basis for their nonresponsiveness. The failure of antigen presentation or T cell help is consistent with recessive inheritance of nonresponsiveness and suggests that response is dominantly inherited.

Lack of immune potentiation by complexing HBsAg in a heat-inactivated hepatitis B vaccine with antibody in hepatitis B immunoglobulin

In a randomized, dose-response study among 305 health care workers, we examined whether the immunogenicity of a heat-inactivated hepatitis B vaccine could be enhanced when HBsAg was complexed by anti-HBs contained in hepatitis B immunoglobulin either at equivalent proportions or at 10-fold antigen excess. The dose of HBsAg in the control vaccine as well as in the two complexed vaccine preparations could be reduced from the standard value (3 micrograms) to 0.6 micrograms per injection without affecting the antibody response in the vaccinees. Still lower dosages of HBsAg in the three vaccine preparations induced significantly lower but comparable anti-HBs responses. These results indicate that, in man, using a heat-inactivated plasma vaccine, addition of anti-HBs contained in hepatitis B immunoglobulin does not potentiate the immunogenicity of HBsAg.

In vitro immune responses to hepatitis B surface antigen (Pre-S2 and S) following remote infection by hepatitis B virus in humans

In this report we evaluate the human immune response to hepatitis B surface antigen (HBsAg) following remote infection with hepatitis B virus (HBV). HBsAg-reactive lymphocytes can be readily demonstrated in the peripheral blood of individuals with established immunity following infection with HBV. In vitro stimulation with small doses of plasma-derived HBsAg, yeast-derived HBsAg (S region) or pre-S2 peptide will induce specific IgG to HBsAg (anti-HBs) in the absence of a polyclonal increase in total IgG. The pre-S2 peptide will stimulate, in a T cell-dependent fashion, the in vitro production of anti-HBs with specificity for the S domain. This anti-HBs production is mediated by pre-S2-stimulated soluble T-cell factors. Peripheral blood mononuclear cells from individuals with established immunity proliferate to the yeast-derived HBsAg but not to the plasma-derived HBsAg or pre-S2 peptide. The chronic HBsAg carriers do not produce anti-HBs following stimulation with HBsAg regardless of the source or component of antigen used. Different study protocols failed to demonstrate HBsAg-specific responses in the peripheral blood mononuclear cells of chronic carriers.

Presentation of an immunodominant T-cell epitope of hepatitis B surface antigen by the HLA-DPw4 molecule

Human T cells that recognize a major epitope of the hepatitis B surface antigen were studied for their ability to react with antigen when presented by mouse fibroblasts that express class II products of the human major histocompatibility gene complex after gene transfection. L cells expressing HLA-DPw4, but not those expressing HLA-DR4 or HLA-DR7, induced strong proliferative responses of antigen-specific T cells to either hepatitis B surface antigen or the synthetic peptide S1d, which bears the immunodominant T-cell epitope. These results identified a genetic restriction element of human helper T-lymphocyte responses to a major antigenic determinant of hepatitis B virus and might be important in the design of subunit vaccines to this pathogen. Peptides that induce T-cell responses that are restricted by a frequently encountered major histocompatibility complex molecule in the general population such as DPw4 would be ideal candidates as subunit vaccines.

Induction of the in vitro anti-HBs response by hepatitis B surface antigen

The production in vitro of antibody to hepatitis B surface antigen by peripheral blood mononuclear cells of healthy volunteers was studied after each of the three doses of hepatitis B vaccine. An in vitro hepatitis B surface antigen antibody response was successfully induced in 12% of the specimens taken over a 7 month period. The response to this antigen was induced in additional samples if cells had been treated previously with anti-CD4 and complement or anti-CD8 and complement prior to culture initiation. The addition of interleukin 2 could also induce the formation of antibodies to hepatitis B surface antigen. The results suggest that the antibody response to hepatitis B surface antigen is complex and varies depending on the individual and time of sampling.

Inhibitory effects of monoclonal antibodies to a synthetic peptide of influenza haemagglutinin on the processing and presentation of viral antigens to class II-restricted T-cell clones

Monoclonal antibodies (mAb) prepared against a synthetic peptide of influenza virus haemagglutinin (HA), containing a known T-cell determinant, were used to examine the mechanism of antigen-induced activation of HA-specific class II-restricted T-cell clones. Previous studies had shown that T-cell clones, established from mice primed by infection with influenza virus, recognize variable antibody binding region of HA, including a determinant formed from residues within the sequence HA1 48-68. MAb to the synthetic peptide, p48-68, recognized purified HA and whole virus in an ELISA, and their specificity pattern for natural variant viruses was similar to that described for the T-cell clones specific for the same peptide. The anti-peptide mAb inhibited peptide or virus-induced proliferation of the peptide specific T-cell clones (but has no effect on a unrelated HA-specific clone), whereas mAb to the native HA molecule inhibited virus but not peptide-induced T-cell activation. In addition, the anti-peptide mAb showed significant inhibition of T-cell proliferation to peptide or virus pulsed antigen-presenting cell (APC). The results suggest that the anti-HA mAb affect antigen induced T-cell activation simply through blocking virus uptake by the APC, whereas the anti-peptide antibodies, which appear to recognize the same determinant on the peptide and the processed antigen, mediate their effect at the level of antigen presentation.

Defect in the membrane expression of high affinity 72-kD Fc gamma receptors on phagocytic cells in four healthy subjects

Three different receptors for the Fc portion of IgG (FcR) have been characterized on human leukocytes. We have identified four healthy members of one family, whose blood phagocytic cells lack functional 72 kD high-affinity FcRI. Their monocytes were unable to bind the Fc portion of mouse (m)-IgG2a and of monomeric human IgG, and they were unreactive with two anti-FcRI monoclonal antibodies. Thus, FcRI is either absent, expressed at very low density, or is so structurally altered as to be unable to bind both its ligand and the anti-FcRI antibodies. The failure to bind the Fc portion of mIgG2a underlies the previously reported inability of these monocytes to support T cell mitogenesis on OKT3 stimulation. FcRI was not inducible upon incubation of their monocytes or neutrophils in gamma interferon. However, their monocytes were able to bind aggregated human IgG, and to phagocytose IgG-coated particles in vitro. Both functions could be blocked with a monoclonal antibody to the 40-kD low-affinity FcRII and therefore apparently were mediated exclusively through FcRII. This also demonstrates that FcRII can mediate phagocytosis independently. Despite the FcRI defect, these subjects had no circulating immune complexes, no evidence of autoimmune pathology and no increased susceptibility to infections.

B-T lymphocyte interactions in experimental autoimmune myasthenia gravis: antigen presentation by rat/mouse hybridoma lines secreting monoclonal antibodies against the nicotinic acetylcholine receptor

Many, but not all rat/mouse B hybridoma cells, producing monoclonal antibodies against determinants on the nicotinic acetylcholine receptor (AChR) of the electric organ of Torpedo californica, were able to immunologically present antigen to AChR-specific, Ia-compatible CD4+ T lymphocyte lines. Most of the hybridomas presented AChR in a privileged manner, i.e. they present AChR even more effectively than macrophages or dendritic cells. However, in the presentation of antigens other than AChR, they were inferior to macrophages. Moreover, some hybridomas were able to present AChR not only in soluble state, but also in membrane vesicles. Privileged presentation of AChR by hybridomas depended on the reactivity of the secreted immunoglobulins with epitopes of the AChR alpha chain, and on the expression of major histocompatibility complex class II antigens on the hybridoma cell surface. There was, however, no quantitative correlation between the actual AChR presentation capacity of one clone and the density of its surface Ia. Neither fine specificity nor isotype of hybridoma immunoglobulin are critical in determining privileged AChR presentation. We postulate that different hybridomas vary in their ability to take up soluble and particulate antigen, to process and to re-express them on the cellular membrane. This capacity may determine their efficiency to present antigen to T cells.

In vitro induction of HBsAg-specific CD8 CD11 human suppressor T cells

Anti-hepatitis B surface (HBs) antibodies have been induced in vitro by human peripheral blood mononuclear cells (PBMC) from individuals immunized with hepatitis B surface antigen (HBsAg). Anti-HBs antibody production is antigen-specific, T-cell dependent, class II MHC-restricted and requires de novo synthesis. Furthermore, HBsAg-specific CD8 suppressor cells can also be induced in vitro after challenge with high antigen doses. Antigen presenting cells (APC) are required for the induction of suppression. These suppressor cells are antigen-specific since they do not suppress the antibody response to tetanus toxoid. Antigen-specific suppression is inhibited by cytotoxic treatment of CD8 CD11 cells with OKM1 monoclonal antibody (MoAb) and complement, suggesting that these suppressor CD8 cells may represent granular lymphocytes. Addition to cultures of high concentrations of a recombinant human IL-2 dose not affect suppression, ruling out the adsorption of IL-2 by suppressor cells as a possible mechanism for suppression.

Modulation of the immunological response to hepatitis B virus by antibodies

Antibodies to HBsAg of IgG class enhanced the helper activity of a human T cell clone to promote the in vitro synthesis of immunoglobulins by autologous B lymphocytes. Using two different assay systems, the effect of antigen-specific antibodies on the helper function of a HBsAg-reactive T cell clone was studied. The monoclonal antibody to HBsAg A5C3 (IgG) increased significantly the T cell-dependent production of immunoglobulins by Staphyloccocus aureus-stimulated autologous B lymphocytes. Furthermore, the results obtained with a different type of assay showed that A5C3 also increased the synthesis of antibody to HBsAg by the autologous B cells in the presence of HBsAg and the helper T cell clone. On the other hand, when the monoclonal antibody to HBsAg of IgM class, H5D3 or the F(ab')2 fragment of A5C3 were tested, no significant enhancement of the helper activity of the T cell clone was observed. Experiments performed in mice showed that the in vivo antibody to HBsAg response to low concentrations of HBsAg was significantly enhanced by mixing this antigen with monoclonal antibody to HBsAg of IgG class. No effect was observed when a monoclonal antibody to HBsAg of IgM class was used to prepare the immune-complexed immunogen. The results presented here suggest that antibodies play a critical role in their own production through regulating the activity of helper T cells. This phenomenon might contribute to the increased antibody synthesis of in vivo secondary immune responses and could be of use in designing more efficient vaccine programs in man.

Antigen presentation by specifically sensitized macrophages in interferon-gamma induction

Antigenic stimulation of specifically sensitized T lymphocytes to interferon-gamma (IFN-gamma) production requires the presence of macrophages. This study examines the ability of peritoneal macrophages from immunized mice to present the antigen to antigen-specific lymphocytes. Such cells presented purified protein derivative (PPD) of tuberculin at concentrations as low as 0.1 micrograms/ml to sensitized T lymphocytes. In contrast, peritoneal macrophages from unimmunized animals required 1,000-fold higher concentrations of antigen to stimulate the same lymphocytes. The presentation of low concentrations of antigen by macrophage from immunized animals was significantly blocked by anti-immunoglobulin antibody, indicating that the surface immunoglobulin receptors were critically involved in this phenomenon. These results suggest that surface immunoglobulins serve to focus antigens onto specific macrophages and that such cells are highly efficient at presenting linked antigenic determinants to T cells. The implication of these findings for the mechanism of IFN-gamma induction are discussed.

Inhibition and enhancement of in vitro helper activity of apocytochrome c-specific murine T cell populations and clones by anti-apocytochrome c-specific monoclonal antibodies

A murine monoclonal antibody (mAb) specific for apocytochrome c was found to be able to either inhibit or enhance the helper activity of mouse apocytochrome c-specific T cell clones and populations in a hapten (trinitrophenyl)-carrier (apocytochrome c) system of T-B cell cooperation. This effect of the mAb was carrier specific, could not be ascribed simply to a shift in the kinetics of the antibody response and was observed using apocytochrome c T helper cells of different mouse haplotypes. In addition, the anti-apocytochrome c mAb was able to inhibit specific T helper cell activity even when the T cells were triggered with antigen-presenting cells pulsed with antigen. Taken together, these results suggested that the mAb was inhibiting helper activity due to its ability to modify the interaction between T cells and antigen-presenting cells.

Presentation by peritoneal macrophages: modulation by antibody-antigen complexes

The effects of immune complex formation on presentation was studied. Immune complexes between an IgG2a monoclonal anti-DNP antibody and TNP-KLH were produced, and the presentation of the carrier molecule by peritoneal macrophages to KLH-primed T cells was monitored. Complex formation was found to enhance the proliferative response of the T cells. This enhancement was specific, was not mediated by lymphokine release, and required antibody with an intact Fc portion. The significance of these results in terms of immune regulation and antigen presentation is discussed.

Amplification of rabies virus-induced stimulation of human T-cell lines and clones by antigen-specific antibodies

The effect of antigen-specific antibodies on the response of human T-cell lines and clones to rabies virus was studied. Plasmas from rabies-immune vaccine recipients, but not those from nonimmune individuals, enhanced the proliferative response of rabies-reactive T cells to whole inactivated virus or to the purified glycoprotein and nucleocapsid from the rabies virion. Rabies-immune plasma also increased the antigen-induced production of gamma interferon by the rabies-specific T-cell lines. Experiments performed on T-cell clones specific for either rabies glycoprotein or nucleocapsid showed that immune plasma as well as antiglycoprotein and antinucleoprotein murine monoclonal antibodies possessed the capacity to increase significantly the antigen-induced proliferative responses of these clones. The overall results indicate that this in vitro effect of antigen-specific antibodies on the response of regulatory T lymphocytes to rabies virus could be an important factor in the development of effective immune responses in vivo to rabies virus.

Regulation of the human immune response to HBsAg: effects of antibodies and antigen conformation in the stimulation of helper T cells by HBsAg

The role of accessory cells (antigen-presenting cells) in binding HBsAg in the response of human T cells to this antigen was studied. Antibodies to HBsAg of IgG class increased significantly the amount of HBsAg that was captured and internalized by accessory cells in vitro. On the other hand, antibodies to HBsAg of IgM class or the F(ab')2 and Fab fragments of antibodies to HBsAg of IgG class did not modify the amount of HBsAg associated to these cells. HBsAg that was subjected to various denaturing treatments (acid, organic solvents, urea and heat) was compared for its capacity to react with antibody to HBsAg and stimulate the response of helper T lymphocytes. Results presented here indicate that HBsAg denatured by treatment with formic acid was captured by accessory cells and presented to the T cells much more efficiently than the native HBsAg. These results suggest that the response of helper T lymphocytes to some antigens such as HBsAg can be affected greatly by the presence of antibodies or the antigens' conformation.

HBsAg-serum protein complexes stimulate immune T lymphocytes more efficiently than do pure HBsAg

HBsAg from plasma of chronic hepatitis B carriers was purified by affinity chromatography using a mouse monoclonal antibody specific for HBsAg. Elution with buffer at two different pH values separated HBsAg into two fractions: one contained high amounts of immune complexes associated with HBsAg; the other contained larger quantities of the HBsAg polypeptides P24 and GP27 and only small amounts of immunoglobulin. When compared for effects on stimulating the proliferative response of freshly isolated lymphocytes and an HBsAg-specific T cell clone, the HBsAg fraction containing a high proportion of immunoglobulin was much more potent than HBsAg with low amounts of immunoglobulins or pure HBsAg, which was isolated from the culture supernatant of the human hepatoma cell line (PLC/PRF/5). The plasma-derived HBsAg with low amounts of complexed immunoglobulins became more immunogenic in the presence of an anti-HBsAg monoclonal IgG. The present results, combined with earlier findings, suggest that HBsAg associated with immune complexes is a more potent stimulator of T cells than purer HBsAg preparations due to an increase in the efficiency of monocytes to capture the antigen through binding to immune complexes for subsequent processing and presentation of the antigen. These observations could be of relevance for the preparation of effective hepatitis B vaccines from recombinant DNA and peptide synthesis technologies.