Anti-IL-6 monoclonal antibodies protect against lethal Escherichia coli infection and lethal tumor necrosis factor-alpha challenge in mice

Potentially fatal physiologic and metabolic derangements can occur in response to bacterial infection in animals and man. Recently it has been shown that alterations in the levels of circulating cytokines such as IL-6 and TNF-alpha occur shortly after bacterial challenge. To understand better the role of IL-6 in inflammation, we investigated the effects of in vivo anti-mouse IL-6 antibody treatment in a mouse model of septic shock. Rat anti-mouse IL-6 neutralizing mAb was produced from splenocytes of an animal immunized with mouse rIL-6. This mAb, MP5-20F3, was a very potent and specific antagonist of mouse IL-6 in vitro bioactivity, demonstrated using the NFS60 myelomonocytic and KD83 plasmacytoma target cell lines, and also immunoprecipitated radiolabeled IL-6. Anti-IL-6 mAb pretreatment of mice subsequently challenged with lethal doses of i.p. Escherichia coli or i.v. TNF-alpha protected mice from death caused by these treatments. Pretreatment of E. coli-challenged mice with anti-IL-6 led to an increase in serum TNF bioactivity, in comparison to isotype control antibody, implicating IL-6 as a negative modulator of TNF in vivo. Anti-TNF-alpha treatment of mice challenged i.p. with live E. coli resulted in a 70% decrease in serum IL-6 levels, determined by immunoenzymetric assay, compared to control antibody, thereby supporting a role for TNF-alpha as a positive regulator of IL-6 levels. We conclude that IL-6 is a mediator in lethal E. coli infection, and suggest that antagonists of IL-6 may be beneficial therapeutically in life-threatening bacterial infection.     

Protective effect of monoclonal antibodies on lethal mouse hepatitis virus infection in mice.

Neutralizing and nonneutralizing monoclonal antibodies to the peplomer glycoprotein and nucleocapsid protein of a mouse hepatitis virus (MHV), MHV-NuU, protected mice against lethal MHV-2 challenge. Histopathologically, livers of mice receiving protective antibodies showed some focal necrotic lesions with remarkable cellular infiltration instead of fulminant hepatitis caused by MHV-2.     

Passive immunization protects guinea pigs from lethal toxoplasma infection

Abstract The cellular and humoral interactions that contribute to protective immunity in toxoplasmosis were studied by adoptive transfer of selective cell populations or immune serum and its fractions into normal syngeneic strain 2 guinea pigs. The results of this study with the RH strain of Toxoplasma gondii confirm and extend the findings of previous studies by showing that the passive transfer of parasite-sensitized T cells or of immune serum from previously infected donors protected recipient guinea pigs against lethal toxoplasmosis. An additional key finding was that similar levels of complete protection against lethal infection occurred in guinea pigs receiving partially purified anti- Toxoplasma immunoglobulins or immune cells that had been enriched for B cells prior to transfer. Cells residing in the spleen, lymph nodes and peritoneal cavity, but not the thymus, were equally effective in conferring immunity to challenged recipients. In addition, cell titration experiments revealed that guinea pigs could survive T. gondii infection by infusing them with as little as 2 × 10⁷ sensitized T cells or B cells. Unlike protection mediated by T cells, protection against lethal disease occurring in the B cell recipients was associated with the formation of Toxoplasma antibodies. These findings illustrate the major role of both humoral and cell-mediated immunity in affording protection against toxoplasmosis based on a guinea pig model of the human disease.     

Passive transfer of antibodies protects immunocompetent and imunodeficient mice against lethal Ebola virus infection without complete inhibition of viral replication

Ebola hemorrhagic fever is a severe, usually fatal illness caused by Ebola virus, a member of the filovirus family. The use of nonhomologous immune serum in animal studies and blood from survivors in two anecdotal reports of Ebola hemorrhagic fever in humans has shown promise, but the efficacy of these treatments has not been demonstrated definitively. We have evaluated the protective efficacy of polyclonal immune serum in a mouse model of Ebola virus infection. Our results demonstrate that mice infected subcutaneously with live Ebola virus survive infection and generate high levels of anti-Ebola virus immunoglobulin G (IgG). Passive transfer of immune serum from these mice before challenge protected upto 100% of naive mice against lethal Ebola virus infection. Protection correlated with the level of anti-Ebola virus IgG titers, and passive treatment with high-titer antiserum was associated with a delay in the peak of viral replication. Transfer of immune serum to SCID mice resulted in 100% survival after lethal challenge with Ebola virus, indicating that antibodies alone can protect from lethal disease. Thus antibodies suppress or delay viral growth, provide protection against lethal Ebola virus infection, and may not require participation of other immune components for protection.     

Development and characterization of monoclonal antibodies to Ebola virus glycoprotein

Balb/С mice were immunized with recombinant Ebola virus glycoprotein. Following the selection, screening, and cloning of murine hybridomas, we obtained five genetically stable clones of monoclonal antibodies GPE118 (IgG), GPE274 (IgM), GPE325 (IgM), GPE463 (IgM), and GPE534 (IgG). These antibodies were isolated and purified from the ascitic fluid of Balb/С mice using Protein G affinity chromatography (for IgG) and euglobulin precipitation (for IgM). To select at least three candidate antibodies for testing in biological assays as components of an antibody cocktail for the prophylaxis and treatment of hemorrhagic fever, we carried out an immunochemical analysis of the epitope specificity of the isolated antibodies. Based on the data of immunoblotting and sandwich ELISA, it became evident that the epitope recognized by GPE 534 differs from the epitopes recognized by the monoclonal antibodies GPE 118 and GPE 325. The last two antibodies also have different epitope specificity: it follows from the immunoblotting data and from the data on the binding of these antibodies with the intact and oxidized (partly deglycosylated) recombinant glycoprotein. For the biological activity studies and the development of recombinant counterparts, we selected three candidate high-affinity monoclonal antibodies GPE 534, GPE 118, and GPE 325.     

Raccoon poxvirus recombinants expressing the rabies virus nucleoprotein protect mice against lethal rabies virus infection.

Raccoon poxvirus (RCN) recombinants expressing the rabies virus internal structural nucleoprotein (RCN-N) protected A/WySnJ mice against a lethal challenge with street rabies virus (SRV). Maximum survival was achieved following vaccination by tail scratch and footpad (FP) SRV challenge. RCN-N-vaccinated mice inoculated in the FP with SRV were resistant to infection for at least 54 weeks postvaccination. Protection was also elicited by RCN recombinants expressing the rabies virus glycoprotein (RCN-G). Vaccination with RCN-G evoked rabies virus neutralizing antibody. Rabies virus neutralizing antibody was not detected in RCN-N-vaccinated mice prior to or following SRV infection. Radioimmunoprecipitation assays showed that sera from RCN-N-vaccinated mice which survived SRV infection did not contain antibody to SRV structural protein G, M, or NS. The mechanism(s) of N-induced resistance appears to correlate with the failure of peripherally inoculated SRV to enter the central nervous system (CNS). Support for this correlation with resistance was documented by the observations that SRV-inoculated RCN-N-vaccinated mice did not develop clinical signs of CNS rabies virus infection, infectious SRV was not detected in the spinal cord or brain following FP challenge, and all RCN-N-vaccinated mice died following direct intracranial infection of the CNS with SRV. These results suggest that factors other than anti-G neutralizing antibody are important in resistance to rabies virus and that the N protein should be considered for incorporation with the G protein in recombinant vaccines.     

BCL-2 and BAX protect adult mice from lethal Sindbis virus infection but do not protect spinal cord motor neurons or prevent paralysis

Cellular proteins that regulate apoptotic cell death can modulate the outcome of Sindbis virus (SV) encephalitis in mice. Both endogenous and overexpressed BCL-2 and BAX proteins protect newborn mice from fatal SV infection by blocking apoptosis in infected neurons. To determine the effects of these cellular factors on the course of infection in older animals, a more neurovirulent SV vector (dsNSV) was constructed from a viral strain that causes both prominent spinal cord infection with hind-limb paralysis and death in weanling mice. This vector has allowed assessment of the effects of BCL-2 and BAX on both mortality and paralysis in these hosts. Similar to newborn hosts, weanling mice infected with dsNSV encoding BCL-2 or BAX survived better than animals infected with control viruses. This finding indicates that BCL-2 and BAX both protect neurons that mediate host survival. Neither cellular factor, however, could suppress the development of hind-limb paralysis or prevent the degeneration of motor neurons in the lumbar spinal cord. Infection of BAX knockout mice with dsNSV demonstrated that endogenous BAX also enhances the survival of animals but has no effect on paralysis. These findings for the spinal cord are consistent with earlier data showing that dying lumbar motor neurons do not exhibit an apoptotic morphology. Thus, divergent cell death pathways are activated in different target populations of neurons during neurovirulent SV infection of weanling mice.     

Immunoglobulin A monoclonal antibodies protect against Sendai virus.

Immunoglobulin A anti-Sendai virus HN protein monoclonal antibodies, generated via a mucosal immunization protocol, were shown to neutralize virus in vitro and, when passively administered to the mouse respiratory tract, to protect against Sendai virus in vivo. Thus, immunoglobulin A antibodies by themselves can protect against respiratory virus infection.     

Suppressive oligodeoxynucleotides protect mice from lethal endotoxic shock

Endotoxic shock is a life-threatening condition caused by exposure to bacterial LPS. LPS triggers the release of acute phase, proinflammatory, and Th1 cytokines that facilitate the development of endotoxic shock. Synthetic oligodeoxynucleotides (ODN) expressing suppressive TTAGGG motifs effectively down-regulate the production of proinflammatory and Th1 cytokines elicited by a variety of immune stimuli. The current results demonstrate that suppressive ODN protect mice from LPS-induced endotoxic shock. Underlying this protective effect is the ability of suppressive ODN to bind to and prevent the phosphorylation of STAT1 and STAT4, thereby blocking the signaling cascade mediated by LPS-induced IFN-beta and IL-12. These findings suggest that suppressive ODN might be of use in the treatment of endotoxic shock.     

Functional CD8+ T cell responses in lethal Ebola virus infection

Ebola virus (EBOV) causes highly lethal hemorrhagic fever that leads to death in up to 90% of infected humans. Like many other infections, EBOV induces massive lymphocyte apoptosis, which is thought to prevent the development of a functional adaptive immune response. In a lethal mouse model of EBOV infection, we show that there is an increase in expression of the activation/maturation marker CD44 in CD4(+) and CD8(+) T cells late in infection, preceding a dramatic rebound of lymphocyte numbers in the blood. Furthermore, we observed both lymphoblasts and apoptotic lymphocytes in spleen late in infection, suggesting that there is lymphocyte activation despite substantial bystander apoptosis. To test whether these activated lymphocytes were functional, we performed adoptive transfer studies. Whole splenocytes from moribund day 7 EBOV-infected animals protected naive animals from EBOV, but not Marburgvirus, challenge. In addition, we observed EBOV-specific CD8(+) T cell IFN-gamma responses in moribund day 7 EBOV-infected mice, and adoptive transfer of CD8(+) T cells alone from day 7 mice could confer protection to EBOV-challenged naive mice. Furthermore, CD8(+) cells from day 7, but not day 0, mice proliferated after transfer to infected recipients. Therefore, despite significant lymphocyte apoptosis, a functional and specific, albeit insufficient, adaptive immune response is made in lethal EBOV infection and is protective upon transfer to naive infected recipients. These findings should cause a change in the current view of the 'impaired' immune response to EBOV challenge and may help spark new therapeutic strategies to control lethal filovirus disease.     

Outer membrane protein-specific monoclonal antibodies protect SCID mice from fatal infection by the obligate intracellular bacterial pathogen Ehrlichia chaffeensis

Previous studies of Ehrlichia chaffeensis infection in the mouse have demonstrated that passive transfer of polyclonal Abs from resistant immunocompetent mice to susceptible SCID mice ameliorated infection and disease, even when Abs were administered during established infection. To identify particular Abs that could mediate bacterial clearance in vivo, E. chaffeensis-specific mAbs were generated and administered to infected SCID mice. Bacterial infection in the livers was significantly lowered after administration of either of two Abs of different isotypes (IgG2a and IgG3). Moreover, repeated administration of one Ab (Ec56.5; IgG2a) rescued mice from an otherwise lethal infection for at least 5 wk. Both protective Abs recognized the E. chaffeensis major outer membrane protein (OMP)-1g. Further studies revealed that both Abs recognized closely related epitopes within the amino terminus of the first hypervariable region of OMP-1g. Analyses of human sera showed that E. chaffeensis-infected patients also generated serological responses to OMP-1g hypervariable region 1, indicating that humans and mice recognize identical or closely related epitopes. These studies demonstrate that OMP-specific mAbs can mediate bacterial elimination in SCID mice, and indicate that Abs, in the absence of cell-mediated immunity, can play a significant role in host defense during infection by this obligate intracellular bacterium.     

Human neutralizing monoclonal antibodies of the IgG1 subtype protect against mucosal simian-human immunodeficiency virus infection

Although maternal human immunodeficiency virus type 1 (HIV-1) transmission occurs during gestation, intrapartum and postpartum (by breast-feeding), 50-70% of all infected children seem to acquire HIV-1 shortly before or during delivery. Epidemiological evidence indicates that mucosal exposure is an important aspect of intrapartum HIV transmission. A simian immunodeficiency virus (SIV) macaque model has been developed that mimics the mucosal exposure that can occur during intrapartum HIV-1 transmission. To develop immunoprophylaxis against intrapartum HIV-1 transmission, we used SHIV-vpu+ (refs. 5,6), a chimeric simian-human virus that encodes the env gene of HIV-IIIB. Several combinations of human monoclonal antibodies against HIV-1 have been identified that neutralize SHIV-vpu+ completely in vitro through synergistic interaction. Here, we treated four pregnant macaques with a triple combination of the human IgG1 monoclonal antibodies F105, 2G12 and 2F5. All four macaques were protected against intravenous SHIV-vpu+ challenge after delivery. The infants received monoclonal antibodies after birth and were challenged orally with SHIV-vpu+ shortly thereafter. We found no evidence of infection in any infant during 6 months of follow-up. This demonstrates that IgG1 monoclonal antibodies protect against mucosal lentivirus challenge in neonates. We conclude that epitopes recognized by the three monoclonal antibodies are important determinants for achieving substantial protection, thus providing a rational basis for AIDS vaccine development.     

Exosomes from Plasmodium yoelii-infected reticulocytes protect mice from lethal infections

Exosomes are 30-100-nm membrane vesicles of endocytic origin that are released after the fusion of multivesicular bodies (MVBs) with the plasma membrane. While initial studies suggested that the role of exosomes was limited to the removal of proteins during the maturation of reticulocytes to erythrocytes, recent studies indicate that they are produced by different types of cells and are involved in promoting inter-cellular communication and antigen presentation. Here, we describe the isolation and characterization of exosomes from peripheral blood of BALB/c mice infected with the reticulocyte-prone non-lethal Plasmodium yoelii 17X strain. Importantly, proteomic analysis revealed the presence of parasite proteins in these vesicles. Moreover, immunization of mice with purified exosomes elicited IgG antibodies capable of recognizing P. yoelii-infected red blood cells. Furthermore, lethal challenge of immunized mice with the normocyte-prone lethal P. yoelii 17XL strain caused a significant attenuation in the course of parasitaemia, increased survival time, and altered the cell tropism to reticulocytes. These results were obtained also when the exosomes were isolated from a P. yoelii-infected reticulocyte culture indicating that reticulocyte-derived exosomes carry antigens and are involved in immune modulation. Moreover, inclusion of CpG ODN 1826 in exosome immunizations elicited IgG2a and IgG2b antibodies and promoted survival, clearance of parasites and subsequent sterile protection of 83% of the animals challenged with P. yoelli 17XL. To our knowledge, this is the first report of immune responses elicited by exosomes derived from reticulocytes opening new avenues for the modulation of anti-malaria responses.     

Human anti-plague monoclonal antibodies protect mice from Yersinia pestis in a bubonic plague model

Yersinia pestis is the etiologic agent of plague that has killed more than 200 million people throughout the recorded history of mankind. Antibiotics may provide little immediate relief to patients who have a high bacteremia or to patients infected with an antibiotic resistant strain of plague. Two virulent factors of Y. pestis are the capsid F1 protein and the low-calcium response (Lcr) V-protein or V-antigen that have been proven to be the targets for both active and passive immunization. There are mouse monoclonal antibodies (mAbs) against the F1- and V-antigens that can passively protect mice in a murine model of plague; however, there are no anti-Yersinia pestis monoclonal antibodies available for prophylactic or therapeutic treatment in humans. We identified one anti-F1-specific human mAb (m252) and two anti-V-specific human mAb (m253, m254) by panning a naïve phage-displayed Fab library against the F1- and V-antigens. The Fabs were converted to IgG1s and their binding and protective activities were evaluated. M252 bound weakly to peptides located at the F1 N-terminus where a protective mouse anti-F1 mAb also binds. M253 bound strongly to a V-antigen peptide indicating a linear epitope; m254 did not bind to any peptide from a panel of 53 peptides suggesting that its epitope may be conformational. M252 showed better protection than m253 and m254 against a Y, pestis challenge in a plague mouse model. A synergistic effect was observed when the three antibodies were combined. Incomplete to complete protection was achieved when m252 was given at different times post-challenge. These antibodies can be further studied to determine their potential as therapeutics or prophylactics in Y. pestis infection in humans.     

Protease-deficient herpes simplex virus protects mice from lethal herpesvirus infection.

Null mutants and attenuated mutants of herpes simplex virus (HSV) have been shown to induce immunity against challenge from wild-type virus. Null viruses with a defect in late gene products would be expected to express more viral genes than viruses with defects in essential early gene products and thus induce a better immune response. Herpesviruses encode a late gene product (serine protease) that is autocatalytic and cleaves the capsid assembly protein during viral replication. To determine whether a virus with a mutation in this gene could induce immunity, we constructed a recombinant virus containing the gusA reporter gene in the protease domain of the HSV type 1 UL26 open reading frame (ORF). Consistent with previous results (M. Gao, L. Matusick-Kumar, W. Hurlburt, S. F. DiTusa, W. W. Newcomb, J. C. Brown, P. J. McCann, I. Deckman, and R. J. Colonno, J. Virol. 68:3702-3712, 1994), recombinant virus could be isolated only from helper cell lines expressing the product of the UL26 ORF. Mice inoculated with the recombinant virus were unaffected by doses of virus that were lethal to mice infected with wild-type virus. Mice which were previously inoculated with the recombinant virus were also protected by a subsequent challenge with wild-type virus in a dose-dependent manner. These results indicate that recombinant viruses lacking the protease gene are avirulent but render protection from subsequent challenge.     

Combinations of polyclonal or monoclonal antibodies to proteins of the outer membranes of the two infectious forms of vaccinia virus protect mice against a lethal respiratory challenge

Previous studies demonstrated that antibodies to live vaccinia virus infection are needed for optimal protection against orthopoxvirus infection. The present report is the first to compare the protective abilities of individual and combinations of specific polyclonal and monoclonal antibodies that target proteins of the intracellular (IMV) and extracellular (EV) forms of vaccinia virus. The antibodies were directed to one IMV membrane protein, L1, and to two outer EV membrane proteins, A33 and B5. In vitro studies showed that the antibodies to L1 neutralized IMV and that the antibodies to A33 and B5 prevented the spread of EV in liquid medium. Prophylactic administration of individual antibodies to BALB/c mice partially protected them against disease following intranasal challenge with lethal doses of vaccinia virus. Combinations of antibodies, particularly anti-L1 and -A33 or -L1 and -B5, provided enhanced protection when administered 1 day before or 2 days after challenge. Furthermore, the protection was superior to that achieved with pooled immune gamma globulin from human volunteers inoculated with live vaccinia virus. In addition, single injections of anti-L1 plus anti-A33 antibodies greatly delayed the deaths of severe combined immunodeficiency mice challenged with vaccinia virus. These studies suggest that antibodies to two or three viral membrane proteins optimally derived from the outer membranes of IMV and EV, may be beneficial for prophylaxis or therapy of orthopoxvirus infections.