Comparative evaluation of three recombinant antigen-based enzyme immunoassays for detection of IgM and IgG antibodies to human parvovirus B19

Background: Diagnosis of acute and past infection with parvovirus B19 is based on detection of IgM and IgG antibodies.Objectives: To evaluate two commercial recombinant antigen-based enzyme immunoassay (EIA) test kits for detection of IgM and IgG antibodies to parvovirus B19 and to compare the commercial EIAs to in-house EIA test procedures.Study design: A panel of 121 sera was used to compare the three IgM EIAs. The panel included 84 sera submitted for parvovirus B19 testing and 37 sera that were IgM positive for other viral pathogens. The same serum panel plus an additional 14 sera submitted for B19 testing was used to compare the three IgG EIAs. The commercial EIAs were performed according to manufacturers' instructions. Using the in-house EIA test procedures as the reference, sensitivity and specificity for each of the commercial EIAs was determined.Results: The commercial B19 IgM EIAs showed agreements of 95.0 and 93.4% to the in-house IgM EIA. Compared to the in-house B19 IgM EIA, the commercial B19 IgM EIAs, were 97.4 and 97.5% sensitive, respectively. Specificities were 93.5 and 91.4%, respectively. Sensitivities for the commercial IgG EIAs, compared to in-house IgG EIA, were 88.0 and 85.2%, respectively, and specificities were 94.1 and 98.0%.Conclusion: We found that the commercial parvovirus B19 IgM and IgG EIAs are comparable to standard in-house EIAs and are suitable for testing for B19 antibodies in human sera.     

Etiology of Maculopapular Rash in Measles and Rubella Suspected Patients from Belarus

As a result of successful implementation of the measles/rubella elimination program, the etiology of more and more double negative cases remains elusive. The present study determined the role of different viruses as causative agents in measles or rubella suspected cases in Belarus. A total of 856 sera sent to the WHO National Laboratory between 2009 and 2011 were tested for specific IgM antibodies to measles virus (MV), rubella virus (RV) and human parvovirus B19 (B19V). The negatives were further investigated for antibodies to enterovirus (EV) and adenovirus (AdV). Children of up to 3 years were tested for IgM antibodies to human herpesvirus 6 (HHV6). A viral etiology was identified in 451 (52.7%) cases, with 6.1% of the samples being positive for MV; 2.6% for RV; 26.2% for B19V; 9.7% for EV; 4.6% for AdV; and 3.6% for HHV6. Almost all measles and rubella cases occurred during limited outbreaks in 2011 and nearly all patients were at least 15 years old. B19V, EV and AdV infections were prevalent both in children and adults and were found throughout the 3 years. B19V occurred mainly in 3–10 years old children and 20–29 years old adults. EV infection was most common in children up to 6 years of age and AdV was confirmed mainly in 3–6 years old children. HHV6 infection was mostly detected in 6–11 months old infants. Laboratory investigation of measles/rubella suspected cases also for B19V, EV, AdV and HHV6 allows diagnosing more than half of all cases, thus strengthening rash/fever disease surveillance in Belarus.     

Viral antibodies in infectious mononucleosis

Abstract Patients with Epstein-Barr virus (EBV) infectious mononucleosis (IM) usually develop heterophilic antibodies and some autoantibodies. Antibodies to rubella, measles, adeno-, entero-, herpes simplex, cytomegalo- and varicella-zoster viruses were titrated in sera from IM patients and matched healthy controls using the complement fixation test (CFT) and the haemagglutination inhibition test. Except for herpes simplex virus and cytomegalovirus, the IM sera had significantly higher arithmetical and geometrical mean antibody titres and showed in most cases higher antibody prevalences in the CFT. The titre rise was most pronounced for rubella and measles antibodies, between 2- and 3-fold. There were no cases of very high titres occasionally seen in IM. The IM sera had higher total IgG serum levels than the controls, 17.27 g/1 and 11.8 g/1, respectively ( P < 0.001). The present data show that in addition to previously reported high levels of some autoantibodies and of heterophilic antibodies, there is a more general increase in IgG antibodies to commonly occurring viruses. This increase is most likely due to the polyclonal activation of B-lymphocytes following the binding of EBV to the complement receptor CR2 (CD21). When due consideration is given to the possible occasional occurrence of a false positive rubella IgM test, the raised antibody-titres will most likely not interfere with routine diagnostics.     

Salivary diagnosis of measles: a study of notified cases in the United Kingdom, 1991-3.

OBJECTIVES--To validate a method for salivary diagnosis of measles and to assess the diagnostic accuracy of notified cases of measles. DESIGN--Blood and saliva samples were collected within 90 days of onset of symptoms from patients clinically diagnosed as having measles and tested for specific IgM by antibody capture radioimmunoassay. SETTING--17 districts in England and one in southern Ireland during August 1991 to February 1993. SUBJECTS--236 children and adults with measles notified by a general practitioner. RESULTS--Specific IgM was detected in serum in only 85 (36%) of the 236 cases. In cases associated with outbreaks and tested within six weeks of onset, 53/57 (93%) of samples were IgM positive, thereby confirming the sensitivity of serum IgM detection as a marker of recent infection. The serological confirmation rate was lower in cases with a documented history of vaccination (13/87; 15%) than in those without (70/149; 47%) and varied with age, being lowest in patients under a year, of whom only 4/36 (11%) were confirmed. Measles specific IgM was detected in 71/77 (92%) of adequate saliva samples collected from patients with serum positive for IgM. In cases where measles was not confirmed, 6/101 had rubella specific IgM and 5/132 had human parvovirus B19 specific IgM detected in serum. CONCLUSIONS--The existing national surveillance system for measles, which relies on clinically diagnosed cases, lacks the precision required for effective disease control. Saliva is a valid alternative to serum for IgM detection, and salivary diagnosis could play a major role in achieving measles elimination. Rubella and parvovirus B19 seem to be responsible for a minority of incorrectly diagnosed cases of measles in the United Kingdom and other infectious causes of measles-like illness need to be sought.     

Epstein-Barr virus but not cytomegalovirus is associated with reduced vaccine antibody responses in Gambian infants

Background

Epstein-Barr virus (EBV) and cytomegalovirus (CMV) are persistent herpesviruses that have various immunomodulatory effects on their hosts. Both viruses are usually acquired in infancy in Sub-Saharan Africa, a region where childhood vaccines are less effective than in high income settings. To establish whether there is an association between these two observations, we tested the hypothesis that infection with one or both viruses modulate antibody responses to the T-cell independent meningococcal polysaccharide vaccine and the T-cell dependent measles vaccines.

Methodology/Principal Findings

Infection with EBV and CMV was diagnosed by the presence of virus-specific IgM in the peripheral blood or by the presence of IgG at higher levels than that found in umbilical cord blood. Anti-meningococcus IgG and IgM were quantified by ELISA. Anti-measles antibody responses were quantified by haemagglutinin antibody inhibition assay. Infants infected with EBV had reduced IgG and IgM antibody responses to meningococcal polysaccharides and to measles vaccine. Infection with CMV alone predicted no changes in the response to meningococcal polysaccharide. While CMV alone had no discernable effect on the antibody response to measles, the response of infants infected with both CMV and EBV was similar to that of infants infected with neither, suggesting that the effects of CMV infection countered the effects of EBV on measles antibody responses.

Conclusions

The results of this exploratory study indicate that infection with EBV is associated with reduced antibody responses to polysaccharides and to measles vaccine, but suggest that the response to T-cell dependent antigens such as measles haemagglutinin may be restored by infection with CMV.     

Clinical and immunological effect of intravesical interleukin-2 on superficial bladder cancer

TheBamHI Z EBV replication activator (ZEBRA) protein is involved in the switch from latency to productive cycle of Epstein-Barr virus. A recombinant ZEBRA protein was synthesized and assessed in enzymelinked immunosorbent assay (ELISA) for serum IgG response in nasopharyngeal carcinoma (NPC) patients. In 100 NPC serum samples that were positive for IgA to the EBV viral capsid antigen (VCA), 75% had IgG anti-ZEBRA antibodies. In contrast, only 3/83 (3.6%) serum samples from healthy donors and 2/50 (4%) from other cancers were positive for IgG to ZEBRA. Interestingly, in a selected group of 100 NPC sera negative for IgA to VCA, 25% contained IgG anti-ZEBRA antibodies. This suggests that the ELISA for IgG anti-ZEBRA may also identify earlier cases of NPC not detected by the conventional immunofluorescence test for IgA to VCA.     

Research on Parvovirus B19 infections and chronic articular manifestations in a Tunisian hospital

Parvovirus B19 infection is often associated with acute and chronic joint diseases thus suggesting an etiologic role for the virus in these pathologies. In this work, we looked for a possible correlation between Parvovirus B19 infection and certain types of chronic inflammatory rheumatisms. We therefore, screened a population of 100 patients with different chronic inflammatory rheumatismal affections for serological markers of Parvovirus B19 infection. All patients were Tunisians of both sexes, who presented at the service of Rheumatology of the Charles Nicolle Hospital, Tunis. One hundred blood donors were taken as controls. Specific Immunoenzyme Assays of the ELISA type (Biotrin International, France) were used to detect anti-Parvovirus IgG and IgM. On the other hand, viral DNA was sought by nested PCR in synovial fluid from 14 patients. The data obtained indicate that specific anti-Parvovirus B19 IgG was detectable in the sera of 80.7% of patients and 43% of controls. In contrast, none of the sera was found positive for specific IgM antibodies. Synovial fluid samples could be collected from 14 anti-Parvovirus B19 seropositive patients and were tested for the presence of viral DNA. None of the samples was found positive. The results of our serological study reinforce the hypothesis that Parvovirus B19 infection is associated with rheumatismal joint affections. However, the lack of detectable viral DNA in synovial fluid of the tested seropositive patients points to an indirect role of the virus in these joint disorders.     

Clinical and epidemiological aspects of human parvovirus B19 infection in an urban area in Brazil (Niterói city area,State of Rio de Janeiro,Brazil)

This study was designed to analyse the clinical and epidemiological data from human parvovirus B19 cases in a six-year study of rash diseases conduct in an urban area in Brazil (Niterói city area, State of Rio de Janeiro). A total of 673 patients with acute rash diseases were seen at two primary health care units and at a general hospital. A clotted blood sample was collected from all subjects at the time of consultation. Forty-nine per cent (330 cases) of the patients were negative for dengue, rubella and measles IgM or for low avidity IgG to HHV-6. Of these 330, 105 (31.8%) were identified as IgM positive to parvovirus B19 by using an antibody capture EIA. During the study period, three distinct peaks of parvovirus infection were detected, suggesting that the disease appears to cycle in approximately 4-5 years. B19 infection was characterized by variable combinations of fever, flu-like symptoms, arthropathy, and gastrointestinal symptoms. Frequency of fever and arthropathy was substantially higher in adults, 75% [chi2 (1 D.F.) = 11.39, p = 0.0007] and 62.5% [chi2 (1 D.F.) = 29.89, p = 0.0000], respectively. "Slapped-cheek" appearance and reticular or lace-like rash were seen in only 30.1% of the children. No adult presented this typical rash. The lack of the typical rash pattern in a large proportion of parvovirus B19 and the similarity of clinical manifestations to other rash diseases, specially to rubella, highlight the difficulty of diagnosing B19 infection on clinical grounds alone.     

The role of IgG avidity determination in diagnosis of Epstein-Barr virus infection in immunocompetent and immunocompromised patients

There is a high degree of variability in the serologic response to Epstein-Barr virus (EBV) infection, especially in viral capsid antigen (VCA)-IgM antibodies. Therefore, additional tests are needed to confirm primary infection. We evaluated the value of IgG avidity determination in diagnosis of EBV infection in immunocompetent and immunocompromised patients. A total of 236 serum samples from immunocompetent patients with symptoms suggestive of EBV infection were tested for the presence of VCA-IgM/IgG antibodies and IgG avidity. Using IgG avidity, acute primary infection was confirmed in 56.7% of the immunocompetent patients with positive and in 1.8% of patients with negative VCA-IgM. Recent primary infection was documented in 8.9% of the IgM positive and 3.5% of the IgM negative patients. In patients with indeterminate serology (equivocal IgM), 6.7% were classified by avidity index (AI) as acute primary infection, 10.0% as post-acute and 83.3% as past infection cases. Concerning the 32 immunocompromised patients, recent primary infection was documented in 3 of the 14 IgM positive patients. High AI was detected in 11 of these patients, indicating an IgM response due to reactivation. Determination of IgG avidity in combination with classical serologic markers seems to be a reliable method to confirm primary infection both in immunocompetent and immunocompromised patients. It may be especially useful to differentiate cases of primary infection in patients with undetectable VCA-IgM antibodies or indeterminate routine EBV serology.     

Prevalence of antibodies to specific infectious agents in bovine fetuses from a slaughterhouse in Minnesota

Sera from 486 bovine fetuses, approximately 60 to 270 days of gestation, were collected at slaughter and tested for the presence of immunoglobulins (Ig). One hundred ten (27%) of the sera were positive for IgG and/or IgM. The earliest age at which fetuses tested positive for IgM and IgG was estimated to be 100 and 120 days, respectively. Ig concentration increased with increased age of the fetus. Sera that were positive for Ig were tested for the presence of specific antibodies to five different infectious agents. Bovine parvovirus antibodies were found in 99 of 110 sera (90%) by hemagglutination inhibition (HI) test. However, only 35 (31.8%) of these sera were positive by serum neutralization (SN) test. Antibodies to parainfluenza-3 virus were detected in 30 sera (27%) by HI test and in 20 sera (18%) by SN test. Five (4%) sera contained SN antibodies to bovine viral diarrhea virus. Only one (0.9%) serum sample contained SN antibodies to infectious bovine rhinotracheitis virus. None of the sera had antibodies against five Leptospira spp. Results of this study suggest that bovine parvovirus may be a potential cause of reproductive problems in cattle.     

Simian parvovirus

Parvovirus B19 is currently the only member of theErythrovirusgenus. Recently a second parvovirus, simian parvovirus, was identified in cynomolgus monkeys which also appeared to be highly tropic for erythroid progenitor cells. This review describes the identification of this new arrival parvovirus and summarizes current knowledge of its clinical, molecular and epidemiological features. The virus has many biological similarities to the parvovirus B19 and close homology to the B19 genome at the molecular level, both of which justify the inclusion of this novel virus as a new member of theErythrovirusgenus.     

IgM antibodies to Epstein-Barr virus-associated membrane antigen in sera of infectious mononucleosis patients

By the indirect immunofluorescence technique, IgM antibodies to the cell surface of an Epstein-Barr virus (EBV) producer cell line, P3HR-1, were detected in sera from infectious mononucleosis (IM) patients but not in sera from patients with Burkitt lymphoma or nasopharyngeal carcinoma nor in sera from healthy adult donors having antibodies to EBV-specific viral capsid antigen (VCA). Titers of the IgM antibodies were higher in the earlier stages of IM, a pattern similar to that for IgM antibodies to VCA. The IgM antibodies to the cell surface were identified as being those against the EBV-specific membrane antigen (MA) by the following criteria: (1) The antibodies were reactive to MA-positive cell preparations but to MA-negative cell preparations. (2) Titers of the IgM antibodies were not significantly affected after absorption of sera with sheep red blood cells which could completely eliminate heterophil antibodies in the same sera. Detection of the IgM antibodies to MA may have a particular diagnostic value for providing evidence of a recent EBV infection.     

Association of cytomegalovirus with infantile hepatitis

Infantile hepatitis is occasionally seen in apparently healthy children. In most cases, the etiology of the infection is uncertain. However, cytomegalovirus (CMV), Epstein-Barr virus (EBV), human herpesvirus-6 (HHV-6), human herpesvirus-7 (HHV-7), human parvovirus B19, and TT virus (TTV) are considered to be associated with hepatitis in children. The objective of this study was to investigate the correlations between these viruses and infantile hepatitis. Twenty-six children from 1 to 24 months old (median age, 7 months) who had liver dysfunction of unknown etiology were enrolled in this study. Plasma samples were examined by a real-time PCR assay for CMV, EBV, HHV-6, HHV-7, parvovirus B19, and TTV DNA. The DNA of CMV was detected in the plasma of four patients (15.4%) and was detected significantly more often in the patient group than in the control group. The CMV-infected patients were 1 to 3 months old, which was significantly younger than the remaining patients. The serological findings did not always correlate with the results of the real-time PCR assay. The DNA of TTV was detected in four patients (15.4%), while human parvovirus B19 DNA was detected in three (11.5%). However, the detection frequencies of these viral DNAs were not significantly different from those in the control groups, and some of these patients had co-infections. These results indicate that CMV might be one of the major pathogens responsible for infantile hepatitis; however, serological tests have limited utility for the diagnosis of CMV infection in young children.     

Study of interaction between IgG and IgM antibodies against rubella virus by the immunofluorescence method.

In immunoglobulin fractions or after elimination of IgG by absorption the immunofluorescence test for rubella IgM antibodies is more sensitive than in whole serum. Blocking of IgM activity by IgG antibodies was eliminated when the time of incubation of the serum with virus antigen was prolonged. After prolonged incubation higher titres of rubella antibodies were also obtained in the IgM immunoglobulin fractions. Protein A in Staphylococcus aureus suspension effectively absorbs antibodies of IgG class. The IgM antibody titres in absorbed sera of patients infected with rubella were in some cases 2 to 4 times higher than in unabsorbed sera.     

2001～2011年上海市风疹病毒分子流行病学研究

本研究对2001～2011年本实验室保存的血清标本检测结果为麻疹IgM阴性,风疹IgM阳性病例相对应的咽拭子标本进行风疹病毒（Rubella virus,RV）分离,用RT-PCR方法对细胞培养产物鉴定后扩增病毒E1基因,扩增产物用于核苷酸序列测定,并进行分子流行病学分析。结果表明,60份咽拭子标本共分离到31株RV,获得27株RV的739nt（nt8 731～nt9 469）核苷酸序列,系统同源性分析表明,27株RV分离株分别属于两个不同的基因型,除分离自2011年的11009株、11052株和11106株为2B基因型外,其他分离株均为1E基因型。27株RV分离株大部分的核苷酸突变为无义突变,氨基酸序列高度保守。24株1E基因型分离株中大部分毒株氨基酸序列完全一致,自2001年以来可能有来自同一传播链的RV在持续传播。本研究首次监测到2B基因型RV2011年开始在上海流行,经GenBank核苷酸序列比对发现,其与越南、日本、阿根廷等国家近几年的RV分离株核苷酸序列同源性达99%。由于以前对风疹的监测较少,尚不能证明其来源。     

In situ hybridization for the detection of human parvovirus B19 nucleic acid sequences in paraffin-embedded specimens

Parvovirus infection of pregnant women leading to a transplacentar infection of the fetus may result in hydrops fetalis, and ultimately in intrauterine death of the fetus. In situ hybridization with a biotinylated as well as with a³⁵S-labeled probe for human parvovirus B19 was performed on formalin-fixed paraffin-embedded (FFPE) tissue from a fetus suffering from non-immunologic hydrops fetalis. Histology was suggestive of viral infection probably with human parvovirus. Parvovirus DNA could be detected and precisely localized mainly in the nuclei of erythroid precursors cells within fetal blood vessels of all organs examined. There was no detection of B19 nucleic acid in parenchymal cells of the placenta or the fetal organs, nor within maternal blood cells. These findings are in agreement with the well-known properties of animal parvoviruses to replicate exclusively in proliferating cells. Taking into consideration the problems in diagnosing human parvovirus infection by light microscopy, we conclude that in situ hybridization with an appropriate non-radioactive probe is a valuable, rapid and safe complementary detection method for the diagnosis and study of human parvovirus infections. The³⁵S-labeled probe is more sensitive than the biotinylated probe, but has the disadvantages of lower resolution of the signal, longer duration of the assay, the hazard of radioactivity and the shorter shelflife of the probe.     

The Cytokines Responses against Parvovirus B19 in Miscarriage Women and the Susceptibility of their RhD Blood Type to Contract Parvovirus B19 in South of Iraq

Background:Parvovirus B19 (B19) infection is linked with various diseases. Cytokines play critical roles in cellular response to viral infection. It has also been reported that’s susceptibility of the ABO blood type people to several viral infection. In this study, we evaluated interleukin 6 (IL-6), interleukin 8(IL-8), and interferon gamma (IFN-γ) levels in aborted women infected with parvovirus B19 (B19+/Abr+) and uninfected with B19(B19-/Abr+) in comparison with healthy women (B12-/Abr-) and susceptibility of their RhD blood type to contract B19.Methods:B19+/Abr+ were diagnosed using IgM and IgG antibodies against B19, and the concentrations of IL-6, IL-8, and IFN-γ were determined using enzyme-linked immunosorbent assay (ELISA) test in both B19+/Abr+, B19-/Abr+, and B19-/Abr-. Here, we also collected blood groups, number of abortion, and gestational ages from 200 B19+/Abr+ along with the same number ofB19-/Abr+ and B19-/Abr-.Results:The levels of IFN-γ were higher in serum of B19-/Abr+andB19+/Abr+ group in comparison to B19-/Abr-, while the serum levels of IL-6, IL-8were increased in B19+/Abr+ group in comparisontoB19-/Abr+ and B19-/Abr-. Our analyzed data also showed that aborted women with RhD+ are more susceptible to contract s B19 than people with RhD- blood type.Conclusion:B19 infection may differently modulate the amount of cytokines in the plasma of aborted women. So, it can be suggested that IL-6, IL-8, and IFN-γ potentially useful as markers for inflammation intrauterine. The susceptibility/protection of aborted women against B19 might be determined based on RhD blood type.Key Words: Aborted women, IL-6, IL-8, IFN-γ, Parvovirus B19, RhD blood type     

Performance of the automated COBAS AMPLICOR™ system for the detection of hepatitis C virus RNA

Background: The COBAS AMPLICOR^™ (CA) instrument for the amplification and detection steps of the AMPLICOR^™ molecular diagnostic assays has recently been introduced. The system contains a single thermal cycler with two independently controlled heating/cooling blocks, a pipettor, a magnetic particle washer, a photometer and an incubator.Objective: The performance of the CA instrument was evaluated in a routine diagnostic laboratory for the detection of hepatitis C virus (HCV) RNA. The new system was compared with the corresponding microwell plate assay (AMPLICOR HCV Test).Study design: Routine clinical sera (350) from hemodialysis patients and patients with chronic HCV infection and interferon therapy were studied. If discrepant results were obtained, both assays were repeated (specimen preparation, amplification and detection); in addition, the HCV copy number was determined with the AMPLICOR HCV MONITOR^™ Test.Results: There was a correlation between the CA HCV Test and the AMPLICOR HCV Test in 341 of 350 specimens (97%). After resolution of 9 discrepant results, the CA HCV Test gave a sensitivity of 97.8% and a specificity of 99.4%. The most common reason for discrepant results was a low HCV RNA copy number.Conclusion: The CA system was found to be a labor-saving, fast and reliable instrument for the amplification and detection steps of a RT-PCR molecular assay for detection of HCV RNA.     

检测脊髓灰质炎IgM抗体捕捉法ELISA的建立及其在早期快速诊断中的应用

首次建立了用于脊髓灰质炎快速、分型诊断的血清IgM抗体捕捉法ELISA。检测了52例疑似病人,IgM阳性率为76.9％(40/52),而粪便病毒分离率仅为44.2％(23/52),前者的阳性检出率明显高于后者。做病毒分型诊断结果,与分离病毒中和试验定型的总符合率为92.86％(39/42)。检测601例来自全国各省的脊灰疑似病人血清,其阳性率波动于13％～92.3％,平均为61.1％。阳性率与收集血清的病日相关,发病0～3天收集者,阳性检出率为69.5％,4～25天者为64％,26～54天者为52％,55天以上者则未能检出。本检测方法需时1.5天,简便、敏感、特异,重复性良好,适用于脊灰的早期快速诊断。对其实用性进行了讨论。     

A differential effect of IgM and IgG antibodies on the blastogenic response of lymphocytes to rubella virus

Peripheral blood lymphocytes of rabbits immunized with live rubella vaccine respond to rubella virus antigens in tissue culture with increased DNA synthesis as measured by incorporation of ³H-thymidine. This reaction can be inhibited by rubella antibody. A dose dependent effect was observed when antibodies in whole serum were mixed with virus prior to addition to lymphocyte cultures. When antisera were fractionated and their individual immunoglobulins tested, a paradoxical effect was obtained. Immune IgG although it was highly effective in neutralizing the virus was incapable of inhibiting the lymphocyte response and at times caused an increased response. In contrast, immune IgM which was less efficient in neutralizing virus caused significant suppression of the blastogenic reaction. By themselves these results might have signified that IgG and IgM antibodies have different specificities or different binding properties with respect to viral surface antigens. However, immune complexes consisting of virus and IgM reduced response of both rubella immune and normal rabbit lymphocytes to PHA. This nonspecific inhibitory action required a specific step of antigen and IgM antibody interaction and normal IgM-virus mixtures or mixtures of anti-rubella IgM and poliovirus or influenza virus did not suppress lymphocyte response to PHA. Anti-rubella IgG complexed with rubella virus did not suppress the PHA response. The IgG function was apparently limited to neutralization of the infectivity of rubella virus whereas the major role of IgM was manifested through its suppressive effect on lymphocyte reactions.