Neutralization of vesicular stomatitis virus (VSV) by human complement requires a natural IgM antibody present in human serum

Neutralization of VSV by human serum ws previously shown to involve C1, C2, C3, and C4 of the classical complement (C) pathway. All normal human sera tested were equivalently active in this regard. However, purified C1, C2, C3, and C4 were unable to mediate VSV neutralization. In the present studies an additional factor required for C-mediated neutralization was isolated from normal human serum and identified as a natural IgM antibody specific for a viral encoded antigen. Purified IgM bound to the virus and formed a complex that activated component C1. Normal serum concentrations of purified IgM, C1, C2, C3, C4 neutralized VSV to the same extent as normal serum. Purified IgM did not neutralize VSV alone or in conjunction with C1, C2, and C4. Inclusion of C3 resulted in full neutralization and C3b binding to the virus was demonstrated. Thus, normal human serum contains a natural antibody of the IgM class that is directed toward a viral antigen. The antibody facilitates neutralization by forming an immune complex that activates C1 and thus efficiently initiates the classical pathway at the viral surface. Neutralization occurs with C3b deposition on the viral envelope and probably results from a blanket of C protein that interferes with viral attachment to susceptible cells.     

Herpes simplex virus complement fixing antibody and herpes B virus serum neutralizing antibody in sera of wild and laboratory-bred cynomolgus monkeys

The result of the complement fixation (CF) test for the antibody to herpes simplex virus (HSV) in sera of the cynomolgus monkeys was compared with that of the neutralization test (NS) for the antibody to herpes B virus (HBV) in the same sera. Fifty-seven (74%) of 77 wild-originated monkeys were positive for HSV-CF, while 65 (84%) of the 77 animals were positive for HBV-SN. All of the 57 CF positive cases were also positive for HBV-SN. On the other hand, 30 (75%) of 40 laboratory-bred monkeys had neither HSV-CF antibody nor HBV-SN antibody. Remaining 10 of the 40 laboratory-bred animals were positive for HSV-CF. However, no HBV-SN antibody was detected in nine of the 10 HSV-CF positive animals. These results suggest that the HSV-CF test may be as satisfactory as the HSV-SN test as a practical measure for rough screening of HBV infection in the cynomolgus monkey in laboratories having no containment unit for handling HBV.     

Neutralization of diverse human immunodeficiency virus type 1 variants by an anti-V3 human monoclonal antibody.

The third variable region (V3) of the HIV-1 gp120 envelope glycoprotein is thought to induce potent neutralizing antibodies which are generally defined as type specific and reactive with individual viral isolates. In contrast, the CD4-binding domain is thought to induce neutralizing antibodies that are group specific and capable of neutralizing all isolates of HIV-1. However, in this study, we used a panel of human monoclonal antibodies to these regions of gp120 which displays specificities and neutralizing activities that challenge these tenets. In particular, we used a human monoclonal antibody to the V3 domain with exceptionally potent and broad neutralizing activity against many diverse HIV-1 isolates. The anti-CD4-binding domain antibodies, on the other hand, showed a more restricted pattern of activity.     

A serological survey of influenza a antibody in human and pig sera in Calcutta

A study was undertaken with a view to assess the distinct pattern of sero-prevalence of influenza A viruses in the city of Calcutta population during the years of 1981–90. Concurrently, based on the fact of increasing pig population, a study was carried out to establish the activity of the human influenza A virus among pigs with a view to the potential threat of emergence of a new strain of influenza A virus that may surface following co-infection with swine and human influenza A viruses. The percentage positivity of the H₃N₂ antigen was found to be highest (46%), followed by H₁N₁ (43%), H₂N₂ (35%) and H₀N₁ (19%). A similar pattern was noted with pig sera.     

Natural antibody and complement mediate neutralization of influenza virus in the absence of prior immunity

Early control of virus replication by the innate immune response is essential to allow time for the generation of a more effective adaptive immune response. As an important component of innate immunity, complement has been shown to be necessary for protection against numerous microbial infections. This study was undertaken to investigate the role of complement in neutralizing influenza virus. Results demonstrated that the classical pathway of complement mediated serum neutralization of influenza virus. Although nonimmune serum neutralized influenza virus, the mechanism of virus neutralization (VN) required antibody, as sera from RAG1-deficient mice lacked VN activity; moreover, purified natural immunoglobulin M (IgM) restored VN activity to antibody-deficient sera. The mechanism of VN by natural IgM and complement was associated with virion aggregation and coating of the viral hemagglutinin receptor; however, viral lysis did not significantly contribute to VN. Additionally, reconstitution of RAG1-deficient mice with natural IgM resulted in delayed morbidity during influenza virus infection. Collectively, these results provide evidence that natural IgM and the early components of the classical pathway of complement work in concert to neutralize influenza virus and that this interaction may have a significant impact on the course of influenza viral pneumonia.     

The opsonic activity of complement in sera without antibody

Путем селекции были отобраны штаммы грамотрицательных бактерий (в фазе S), суспензия которых в растворе Ringer-Locke при перфузии не задерживается изолированной печенью. Опсонизио рвание этих штаммов сывороткой, которая не содержит антител, новорожденных поросят, не получавших еще молозива, значительно увеличивает процент задерживаемых бактерий Путем инактивирования компонентов комплемента было доказано, что опсонизирующее действие зависит от функции комплемента, даже если антитела не присутствуют.     

Fine specificity of the in vitro antibody response to influenza virus by human blood lymphocytes

The fine specificity of anti-influenza antibody produced in vitro by human PBM stimulated with different strains of influenza virus was examined by competition binding in solid phase enzyme immunoassay. Most of the antibody produced in vitro is directed to strain-specific or cross-reactive determinants on the hemagglutinin molecule. The extent of cross-reactivity is dependent on the strain of virus used to stimulate PBM as well as the individual tested and presumably on his previous exposure to influenza viruses. PBM from some individuals produced antibody that bound to the stimulating strain of influenza virus but not to other strains of the same subtype. In other individuals, antibody was produced in vitro that cross-reacted with all viruses in the same subtype (e.g., H3N2; A/X31, A/X47, and A/Texas) but did not bind to other (H2N1 or H1N1) subtypes, and in a few individuals, extensive cross-reaction between subtypes was seen. The presence of antibody to hemagglutinin in these culture supernatants was confirmed by competition binding to highly purified hemagglutinin. This in vitro culture system allows the immunologic memory of individuals to a wide range of stimulating virus strains to be examined simultaneously in terms of specificity of the antibody response by human PBM to influenza virus after natural infection or immunization.     

The effect of anti-Anisakis simplex antibody levels on C3 and C4 complement components in human sera

Previously, an in vitro effect was observed on the complement system not only of the excretory-secretory products but also of somatic antigens from L3 Anisakis simplex larvae. In the present work the effect of anti-A. simplex specific antibodies on C3 and C4 levels in human sera was investigated. Up to 309 samples of sera were tested to determine levels of C3 and C4 and anti-A. simplex antibodies, including immunoglobulins IgG, IgM, IgA and IgE. Significant differences were observed between levels of C3 and C4 and all immunoglobulins except for IgE. In the case of immunoglobulins, the probability that an anti-A. simplex positive subject has a C3 deficiency was 3.8 times higher than a subject without specific antibodies. In conclusion, an association between elevated levels of anti-A. simplex antibodies and C3 and C4 deficiency was demonstrated.     

Elucidating the mechanisms of influenza virus recognition by Ncr1

Natural killer (NK) cells are innate cytotoxic lymphocytes that specialize in the defense against viral infection and oncogenic transformation. Their action is tightly regulated by signals derived from inhibitory and activating receptors; the later include proteins such as the Natural Cytotoxicity Receptors (NCRs: NKp46, NKp44 and NKp30). Among the NCRs, NKp46 is the only receptor that has a mouse orthologue named Ncr1. NKp46/Ncr1 is also a unique marker expressed on NK and on Lymphoid tissue inducer (LTI) cells and it was implicated in the control of various viral infections, cancer and diabetes. We have previously shown that human NKp46 recognizes viral hemagglutinin (HA) in a sialic acid-dependent manner and that the O-glycosylation is essential for the NKp46 binding to viral HA. Here we studied the molecular interactions between Ncr1 and influenza viruses. We show that Ncr1 recognizes influenza virus in a sialic acid dependent manner and that N-glycosylation is important for this binding. Surprisingly we demonstrate that none of the predicted N-glycosilated residues of Ncr1 are essential for its binding to influenza virus and we thus conclude that other, yet unidentified N-glycosilated residues are responsible for its recognition. We have demonstrated that N glycosylation play little role in the recognition of mouse tumor cell lines and also showed the in-vivo importance of Ncr1 in the control of influenza virus infection by infecting C57BL/6 and BALB/c mice knockout for Ncr1 with influenza.     

Effect of actinomycin D on immune antibody, normal antibody, and complement

Muschel, Louis H. (University of Minnesota, Minneapolis), Jean L. Jackson, and Karen Schmoker. Effect of actinomycin D on immune antibody, normal antibody, and complement. J. Bacteriol. 91:270-272. 1966.-The effect of actinomycin D on the immune response, when the antibiotic was administered to rabbits simultaneously with antigen, and its effect on naturally occurring levels of antibody and complement were determined. Those amounts of the antibiotic that effected a significant suppression of the immune response against deliberately injected antigens did not cause a decline in levels of naturally occurring antibody. Complement titers were also refractory to the antibiotic.