Polyclonal and monoclonal antibody therapy for experimental Pseudomonas aeruginosa pneumonia.

A human immunoglobulin G preparation, enriched in antibodies to lipopolysaccharide (LPS) Pseudomonas aeruginosa antigens (PA-IGIV) and murine monoclonal antibodies (MAb) to P. aeruginosa Fisher immunotype-1 (IT-1) LPS antigen and outer membrane protein F (porin), were evaluated for therapeutic efficacy in a guinea pig model of P. aeruginosa pneumonia. The concentration of antibodies to IT-1 LPS was 7.6 micrograms/ml in PA-IGIV and 478 micrograms/ml in the IT-1 MAb preparation. No antibody to IT-1 was detected in MAb to porin. For study, animals were infected by intratracheal instillation of IT-1 P. aeruginosa and then treated 2 h later with intravenous infusions of PA-IGIV, IT-1 MAb, or porin MAb. Control groups received intravenous albumin, and routinely died from pneumonia. Both PA-IGIV (500 mg/kg) and IT-1 MAb (greater than or equal to 2.5 mg/kg) treatment resulted in increased survival (P less than 0.01 to 0.001), and also improved intrapulmonary killing of bacteria. Porin MAb failed to protect from fatal pneumonia. IT-1 MAb treatment produced more survivals than did PA-IGIV treatment but only at dosages of MAb resulting in serum antibody concentrations greater than those achieved with PA-IGIV. PA-IGIV and IT-1 MAb demonstrated in vitro and in vivo (posttreatment guinea pig serum) opsonophagocytic activity for the IT-1 challenge strain. However, the polyclonal preparation required complement, whereas the MAb did not. We conclude that passive immunization with polyclonal hyperimmune P. aeruginosa globulin or with MAb to LPS antigens may be useful in the treatment of acute P. aeruginosa pneumonia. The relative efficacies of such preparations may be limited, however, by their type-specific LPS antibody concentrations.     

Monoclonal antibody to human beta interferon: characterization and application

Seven stable mouse hybridomas secreting monoclonal antibodies to human fibroblast beta interferon (IFN-beta) were isolated, all seven of which belonged to IgGl subclass and kappa type. While neutralizing the antiviral activity of human fibroblast IFN-beta, they failed to neutralized both that of human IFN-alpha and human IFN-gamma. These monoclonal antibodies neutralized the antiviral activity of human fibroblast IFN-beta but not that of human IFN-alpha and IFN-gamma. Two of the seven monoclonal antibodies, YSB-1 and YSB-2, showed particularly high neutralization titers in the ascitic fluid. Monoclonal antibodies were purified from cultures of hybridoma grown in a serum-free medium. The purified monoclonal antibodies, YSB-1(5 micrograms/ml) and YSB-2(1 microgram/ml), neutralized IFN-beta from 10EU/ml to 1EU/ml. Human fibroblast IFN-beta was purified to 3.5 X 10(7) IU/mg protein (1.0 X 10(8) IU/mg protein in the peak fraction) by the monoclonal antibody (YSB-2) affinity column chromatography, whereas human recombinant IFN-beta obtained from E.coli was also purified to 6.5 X 10(7) IU/mg protein (1.1 X 10(8) IU/mg protein in the peak fraction) by the monoclonal antibody (YSB-1) affinity column chromatography.     

Release of interleukin-1 beta associated with potent cytocidal action of staphylococcal alpha-toxin on human monocytes.

The pathogenetic relevance of Staphylococcus aureus alpha-toxin in humans has been debated because human cells have been thought to display a natural resistance toward the cytotoxic action of this cytolysin. Following our previous demonstration that human platelets represent sensitive targets for toxin attack, we have now identified monocytes as a second, highly vulnerable human cell species that succumb to attack by low doses (20 ng/ml) of alpha-toxin. The cytotoxic action of alpha-toxin is reflected in a rapid depletion of cellular ATP that is essentially complete within 30 min. The presence of human plasma proteins affords some protection of monocytes against the action of the toxin. In 10% autologous serum, ATP depletion commences at 80 to 300 ng of toxin per ml. Subcytolytic doses stimulate the release of tumor necrosis factor alpha, a process that is slightly accentuated in the presence of 50% serum. Cytocidal toxin doses unfailingly cause the release of large amounts of interleukin-1 beta from cultured cells, with levels of this monokine generally exceeding 10 ng/ml in the cell supernatants 60 min after application of toxin. Initial evidence suggests that this is due to processing of intracellular interleukin-1 rather than to de novo synthesis of the cytokine. All noted effects are abrogated in the presence of a neutralizing monoclonal antibody against alpha-toxin. Through its capacity to provoke cytokine release from monocytes and its attack on platelets, alpha-toxin may initiate cellular events that are relevant to the pathogenesis of staphylococcal infection.     

Identification of measles virus-specific hemolysis-inihibiting antibodies separate from hemagglutination-inhibiting antibodies.

The occurrence of antibodies giving hemolysis inhibition (HLI) but not hemagglutination inhibition (HI) was examined in human convalescent and rabbit hyperimmune sera. HI antibodies, which through their interaction with hemagglutinin components display HLI activity, were removed by absorption with Tween 80-ether (TE)-treated measles virus material. This absorption did not change the titer of non-HI HLI antibodies. After removal of HI antibodies from 16 late measles convalescent sera and three batches of gamma globulin. HLI antibody titers showed a two- to eightfold reduction. The titers of neutralizing antibodies were reduced from 1/4 to 1/20 of the original titers. There was a good correlation between the titers of neutralizing and HLI antibodies both in sera from which HI antibodies had been removed by absorption and in sera spontaneously showing markedly higher HLI than HI antibody titers. HLI antibodies with these characteristics could be identified in HI tests when whole virus instead of TE-treated material was used an antigen and anti-antiserum was added to the tests. In contrast to the situation in human sera, antibodies remaining after removal of HI antibodies from rabbit hyperimmune sera against purified virus particles were detectable in neutralization and HLI tests only in the presence of anti-antiserum. However, virus particles from which the major fraction of all envelope projections had been removed by treatment with 0.004% trypsin induced the production of non-HI HLI antibodies active also in the absence of anti-antiserum. TE and formalin treatment destroyed the hemolytic activity of virus preparations and also their capacity to induce a production of non-HI HLI antibodies.     

Correlation between toxin binding and hemolytic activity in membrane damage by staphylococcal alpha-toxin

The binding of Staphylococcus aureus alpha-toxin to rabbit and human erythrocytes was studied by hemolytic assays and sodium dodecyl sulfate-polyacrylamide gel electrophoresis immunoblotting. Hemolytic assays showed that toxin binding to 10% cell suspensions at neutral pH was very ineffective in the concentration range 3 X 10(-8) to 3 X 10(-7) M (1 to 10 micrograms/ml), and less than 5% of added toxin became cell bound. However, binding was augmented as toxin levels were raised, abruptly increasing to 50 to 60% at 2 X 10(-6) to 3 X 10(-6) M (60 to 100 micrograms/ml). When rabbit erythrocytes were lysed with 1 to 5 micrograms of toxin per ml, both monomeric and hexameric forms of the toxin could be detected on the membranes by sodium dodecyl sulfate-polyacrylamide gel electrophoresis immunoblotting. In contrast, human erythrocytes treated with 1 to 6 micrograms of toxin per ml did not lyse, and membrane-bound toxin was not detectable. When toxin concentrations were raised to 30 to 100 micrograms/ml, human erythrocytes also lysed and toxin hexamers became membrane bound in comparable amounts as on rabbit cell membranes. Lowering the pH led to a marked increase in susceptibility of human, but not rabbit erythrocytes towards alpha-toxin. When human cells were lysed at pH 5.0 with 5 micrograms of toxin per ml, membrane-bound hexameric toxin became detectable. The demonstrated correlation between the presence of hexameric, cell-bound toxin and hemolytic activity supports the channel concept of toxin-mediated cytolysis. The results also show that toxin binding does not exhibit overall characteristics of a simple receptor-ligand interaction.     

Antibody to varicella-zoster virus after passive immunization against chickenpox.

Antibody titers to varicella-zoster virus were measured in varicella-susceptible immunocompromised children 48 h after they received either one of two lots of zoster immune globulin (ZIG) or a selected lot of immune serum globulin (ISG). Globulin was given to modify varicella in these children after exposure to varicella or zoster. Indirect immunofluorescence antibody titers (FAMA) of children after receipt of globulin ranged from less than 1:2 to 1:32. Geometric mean FAMA titers were highest after 1.2 ml of ISG per kg (FAMA titer 1:128) and 0.16 ml of ZIG lot A per kg (FAMA titer 1:1,024). Selected batches of ISG titering 1:128 or greater by FAMA, at a dose of 1.2 ml/kg, may be used to attempt to modify varicella in susceptible high-risk individuals when ZIG is not available.     

Characterization of a human monoclonal immunoglobulin M (IgM) antibody (IgMBEN) specific for Vi capsular polysaccharide of Salmonella typhi.

A search for human monoclonal antibodies to protective antigens of bacteria revealed an immunoglobulin M lambda chain [IgM(lambda); designated IgMBEN] reactive with the Vi capsular polysaccharide of Salmonella typhi. Vi, a linear homopolymer of alpha(1-->4)GalApNAc that is O acetylated at C-3, is a licensed vaccine for typhoid fever. Immunologic properties of IgMBEN were compared to those of burro globulin prepared by intravenous injections of S. typhi (B339-340). IgMBEN and B339-340 yielded identical precipitin lines with Vi by double immunodiffusion. IgMBEN and B339-340 produced similar precipitation results with Vi and its derivatives prepared by de-O-acetylation, carboxyl reduction, and removal or replacement of the N-acetyl at C-2 with O-acetyl. B339-340 yielded maximal precipitation with Vi (0.41 mg of antibody per ml with 1.4 micrograms of Vi); next was carboxyl-reduced, O-acetylated Vi, which precipitated 0.325 mg of antibody per ml with 2.5 micrograms of Vi. IgMBEN yielded maximal precipitation with de-O-acetylated, carboxyl-reduced Vi (approximately 11.0 mg of antibody per ml with approximately 1.3 micrograms of antigen); next were de-O-acetylated Vi (9.89 mg/ml) and Vi (9.19 mg/ml). The precipitin curves and equivalence points of these three antigens were similar. Pneumococcus type 1, which contains GalApNAc, did not precipitate with Vi or its derivatives. These slight differences in specificity between IgMBEN and B339-340 were related to our proposed structure of Vi. We plan to use IgMBEN as a reference for measurement of vaccine-induced Vi antibodies.     

Efficacy of Human Hyperimmune Globulin in Prevention of Haemophilus influenzae Type b Disease in Infant Rats

To determine the protective efficacy of human hyperimmune globulin to Haemophilus influenzae type b disease in an infant rat model, we compared hyperimmune globulin containing 600 μg of anti-polyribophosphate (PRP) antibody per ml to conventional immune globulin containing 66 μg of anti-PRP antibody per ml. The hyperimmune globulin was fractionated from the pooled plasma of 55 adult donors immunized with PRP, the capsular polysaccharide of H. influenzae type b. The disappearance of passively administered antibody was biphasic, with a linear first-order disappearance curve during the first 7 days. The initial half-life for anti-PRP antibody was 2.38 days in rats nasally colonized but not detectably bacteremic with H. influenzae type b and significantly longer (half-life, 10.3 days; P < 0.01) in noncolonized animals. Hyperimmune globulin afforded 10 times the protection of conventional globulin against bacteremia and meningitis. Globulin depleted of anti-PRP antibody offered no protection. The initial serum antibody levels and the levels during the 8-day observation period predicted protection. Rats maintaining serum antibody levels greater or equal to 50 ng/ml to day 8 had a 10% bacteremia and 5% meningitis incidence in contrast with 95% bacteremia (P < 0.001) and 55% meningitis (P < 0.001) in rats with less than 50 ng of anti-PRP antibody per ml. We conclude that studies of the pharmacology and efficacy of hyperimmune globulin are warranted in high-risk children unable to respond to active immunization.     

Antidiphtheria antibody responses in patients and carriers of Corynebacterium diphtheriae in the Arkhangelsk region of Russia

Diphtheria is under control in industrialized countries. However, single cases and outbreaks still occur and the disease is not completely understood. Forty-three individuals suspected of having diphtheria who were referred to the Infectious Disease Hospital of Arkhangelsk from December 1994 to March 1995 were included in this study. Fifteen patients were diagnosed as having diphtheria and received equine hyperimmune antidiphtheria toxin antiserum, and 28 were diagnosed as carriers, 12 with nondiphtherial tonsillitis or pharyngitis and 16 without symptoms. Serum samples were obtained on admission and during the course of the disease or during follow-up of carrier status. Samples were analyzed for antibodies against diphtheria toxin with both an in vitro neutralization test (NT) and a human-specific enzyme immunoassay. All of the cases but one were confirmed by a positive culture. Twelve patients had pharyngeal diphtheria, and three had combined laryngeal and pharyngeal disease. Half of the patients had life-threatening disease, and one died. On admission, the median antibody titers measured with the NT were 0.085 IU/ml for the patients, 5.12 IU/ml for the symptomatic carriers, and 10.24 IU/ml for the healthy carriers. All of the diphtheria patients but one and nine of the carriers (six symptomatic and three healthy) had increased antibody levels during the first 7 to 10 days after admission. No obvious correlation was revealed between the antibody level or its kinetics and the course of the disease. Antibody levels on admission of >1 IU/ml were associated with a low risk of diphtheria.     

Decrease of HLA-DR antigen expression by human monocytes during cultivation in absence of exogenous or endogenous interferon-gamma

The kinetics of HLA-DR antigen expression by human peripheral blood monocytes during cultivation in vitro was studied. Immediately after separation by glass adherence, about 60% of monocytes expressed DR antigens as judged by indirect fluorescence staining with a monoclonal antibody (BL-DR/1). Monocytes carefully depleted of lymphocytes, gradually lost their DR antigens during cultivation in the absence of exogenous interferon-gamma (IFN-gamma). However, addition of a few lymphocytes to the adherent cells prevented the decrease of DR antigen expression. Furthermore, it was shown that doses as low as 1 IU/ml of IFN-gamma are sufficient to induce DR antigen expression by cultured monocytes. Experiments with cyclosporin A suggest that lymphocytes contaminating the monocyte preparations can produce spontaneously sufficient amounts of IFN-gamma for maintenance of the DR antigens on monocytes.     

Release of cytokines induced by Salmonella typhimurium porins.

Salmonella typhimurium SH5014 porins induce the release of tumor necrosis factor alpha (TNF-alpha), interleukin 1 alpha (IL-1 alpha), and IL-6 by human monocytes and of gamma interferon (IFN-gamma) and IL-4 by human lymphocytes. Porins at 1 microgram/ml induce the greatest release of TNF-alpha, IL-1 alpha, and IL-6 by monocytes and of IL-4 by lymphocytes, while porins at 5 micrograms/ml induce the greatest release of IFN-gamma by lymphocytes. The R form of lipopolysaccharide (LPS-R) induces the greatest release of TNF-alpha and IL-1 alpha by monocytes when used at a low concentration (1 microgram/ml). At higher concentrations (5 and 10 micrograms/ml, respectively), LPS-R induces the maximal release of IL-6 from monocytes and the maximal release of IL-4 from lymphocytes. The S form of LPS (LPS-S) induces the greatest release of TNF-alpha, IL-1 alpha, and IL-6 by monocytes and that of IL-4 by lymphocytes when used at a concentration of 1 microgram/ml. After stimulation with LPS-S, the largest quantity of TNF-alpha and IL-1 alpha released was less than that obtained after stimulation with LPS-R at the same concentration, while the quantity of IL-6 released was found to be slightly higher than that obtained after stimulation with porins or LPS-R. LPS-S (1 microgram/ml) induces IFN-gamma release from lymphocytes in notably smaller quantities than that obtained with LPS-R and slightly larger quantities than that obtained with porins. The preparation of porins used was found to be contaminated with 10 pg of LPS per 10 micrograms of porins, a quantity which was found to have no biological effect; furthermore, porin preparations with the addition of polymyxin B gave the same results.     

The detection of IgE-secreting cells in the peripheral blood of patients with atopic dermatitis.

We report, for the first time, the identification of IgE-secreting cells in human peripheral blood with an ELISA plaque assay that detects the fingerprint of individual IgE-secreting cells. No IgE-secreting cells could be detected in the blood of normal individuals (IgE, less than 100 IU/ml) or atopic patients (IgE, less than 1000 IU/ml), but in patients with atopic dermatitis (AD) whose IgE was greater than 2000 IU/ml, there was an average of 49 +/- 9 IgE-secreting cells per 10(6) peripheral blood mononuclear cells (PBMNCs). The rate of IgE production per cell per day from the PBMNCs of patients with AD varied from 0.051 to 0.628 IU/ml, and the number of IgE-secreting cells was positively correlated with the serum-IgE levels of these subjects (r = 0.74; p less than 0.001) and the amount of IgE detected in the culture supernatant (r = 0.085; p less than 0.02). Secretion of IgE by these cells could be completely inhibited (96.2% +/- 3%) by the addition of 75 micrograms of cyclohexamide to the cultures. Preformed intracellular IgE comprised 10% of the IgE detected in the supernatants of 7-day cultures. PBMNCs from patients with AD depleted of monocytes by adherence and T cells by E rosetting, all contained some detectable IgE-secreting cells, whereas isolated T cells and monocytes did not, supporting the view that cells secreting IgE that were detected were indeed B cells.     

Detection of antibodies to gangliosides and glycolipids in various intravenous immunoglobulin (IVIg) preparations

The aim of this study was to examine the presence of antibodies to GM1 and sulfatide in various IVIg preparations. Five brands of commercially available human IVIg (Sandoglobulin, Isiven, Cytogam, Omrigam and Cutter) were examined and compared. Serial dilutions of each of the above preparations were prepared at a working range of 0.009 to 25.0 mg/ml IVIg, and screened by a standard 96-well microplate EIA for autoantibodies to the ganglioside GM1 and to the glycolipid sulfatide. The various IVIg preparations (Omrigam, Cytogam, Sandoglobulin, Isiven), except for Cutter IVIg, contained low to medium titers of the autoantibodies tested. Omrigam and Cytogam IVIg contained low titer of antibodies to GM1, and medium-titer of antibodies to sulfatide, whereas Sandoglobulin and Isiven contained only low-titer of autoantibodies to sulfatide. The presence of natural autoantibodies to myelin in human sera may explain the presence of the tested antibodies within IVIg preparations. Measurements of antibodies to ganglioside and glycolipid in sera of Guillain-Barré patients immediately following IVIg, would probably not reveal antibody decrease. Alternatively, long-term (several weeks) follow-up of titers might result in their modification due to inhibition of antibodies production by IVIg.     

Enzyme-linked immunosorbent assay for titration of Haemophilus influenzae capsular and O antigen antibodies.

The enzyme-linked immunosorbent assay (ELISA) was elaborated for the detection of immunoglobulin M (IgM) and IgG antibodies against capsular and O antigens of Haemophilus influenzae. Purified capsular polysaccharide and lipopolysaccharide were used as antigens, with optimal coating concentrations being about 50 and 100 micrograms/ml, respectively. The antibody content was expressed as the highest serum dilution (-log10) showing an absorbance of 0.2 above the background level. The titers of hyperimmune sera (reference sera) ranged between 5 and 7 -log10. The sensitivity of the method was about 80 ng/ml with regard to anticapsular antibodies and 3 to 5 ng/ml with regard to anti-lipopolysaccharide antibodies. For detection of antibodies against capsular polysaccharide in sera obtained after primary immunization, ELISA was about 100-fold more sensitive than the indirect hemagglutination assay, whereas in hyperimmune sera, ELISA was about 10-fold more sensitive than the indirect hemagglutination assay. The sensitivity of ELISA for detecting anticapsular antibodies after primary and booster immunizations was 50-fold higher than that of the bactericidal assay using capsulated bacteria, whereas the sensitivity of the two methods was the same when hyperimmune sera were tested. ELISA performed with lipopolysaccharide as the antigen was about 50- and 150-fold more sensitive than the complement fixation and bactericidal assays tested with noncapsulated variants after primary injection and hyperimmunization, respectively.     

Evaluation of neutralizing antibodies to type A, B, E, and F botulinum toxins in sera from human recipients of botulinum pentavalent (ABCDE) toxoid.

Twenty-five serum specimens from personnel immunized with botulinum pentavalent toxoid (ABCDE) had titers of neutralizing antibodies to type A (5.7 to 51.6 IU/ml), type B (0.75 to 18 IU/ml), and type E (0.61 to 10 IU/ml) botulinum toxins. Titers for one type could not be used to predict titers for another type in individuals receiving the toxoid. Cross-neutralizing antibodies to type F botulinum toxin were not detected (less than 0.0125 IU/ml).     

Core promoter mutations (A(1762)T and G(1764)A) and viral genotype in chronic hepatitis B and hepatocellular carcinoma in Guangxi,China

Inhibition of virus-induced intracellular signaling pathways and viral infectivity are our ultimate goals in the development of effective antiviral agents to control human cytomegalovirus (HCMV) infections. The HCMV hyperimmune globulin may meet such criteria. In a human embryonic lung (HEL) fibroblast culture model, pretreatment of Towne strain HCMV with HCMV hyperimmune globulin was shown to inhibit viral infectivity successfully, as measured by a standard plaque assay. The extracellular viral titers and extracellular viral DNA, as measured by plaque assay and PCR, respectively, were also decreased. In addition, the HCMV hyperimmune globulin prevented HCMV from inducing the intracellular activation of NF-kappaB, Sp-1, and PI3-K signaling pathways. The PI3-K pathway was examined by following phosphorylation (activation) of two of its downstream kinases, Akt and p70S6K. HCMV hyperimmune globulin also prevented the production of immediate early, early, and late viral proteins. These studies show that HCMV hyperimmune globulin neutralization of HCMV prevents the earliest known events observed after viral envelope glycoproteins bind their cell membrane receptors, i.e., NF-kappaB, Sp-1 and PI3-K activation. This suggests that HCMV hyperimmune globulin not only can inhibit viral infectivity, but can also prevent the abnormal cellular signaling that may induce unwanted cellular proliferation or cytokine synthesis.     

Comparison of the neutralizing and ELISA antibody titres to human cytomegalovirus (HCMV) in human sera and in gamma globulin preparations

Administration of anti-cytomegalovirus gamma globulin has been reported to prevent acute human cytomegalovirus (HCMV) infection in immunocompromised patients. Most likely the gamma globulin acts by its neutralizing activity. However, the antibody titer to HCMV in hyperimmune gamma globulin is usually detected by an enzyme immunoassay (ELISA). We, therefore, compared the ELISA titres with the neutralizing antibody titres in the sera of blood donors and in hyperimmune gamma globulins. A poor correlation between both titres was found. Gamma globulin preparations with identical ELISA titres clearly differed in the neutralizing titre. If neutralization is the important mechanism by which the hyperimmune gamma globulins work, our results would favour a routine testing of the neutralizing antibody titre in HCMV hyperimmune gamma globulins.     

Detection and neutralization of bovine tumor necrosis factor by a monoclonal antibody.

Monoclonal antibodies (MAbs) have been produced which are specific for bovine tumor necrosis factor (TNF). MAb BC9 detects bovine TNF in a radioimmunoassay with a detection limit of 24 pg/ml. BC9 also neutralizes the in vitro biological function of bovine recombinant TNF. The activity of 250 ng TNF/ml was entirely neutralized by 1% ascitic fluid. When ascites was added at a saturating concentration (10% ascitic fluid), up to 25 micrograms TNF per ml was neutralized. The neutralizing effect of BC9 was seen in cytotoxic assays using L929 cells and WEHI 164 clone 13 cells. The cytotoxic activity of supernatants from in vitro activated bovine monocytes was entirely blocked by BC9.     

Lymphocyte stimulation in vitro by orosomucoid glycoprotein

Mitogenesis of human peripheral blood lymphocytes as measured by the uptake of [3H]thymidine was stimulated in vitro by pure orosomucoid glycoprotein when used at concentrations that are considerably lower than the physiological plasma level. The lymphocyte cultures stimulated with PHA or PWM were not affected by low concentration (67 micrograms/ml), but they were mildly suppressed by high concentration (1 mg/ml) of this glycoprotein. The stimulatory response was relatively greater with fractionated T cells than the non-T cells (B cells and monocytes). At 50 micrograms/ml concentration of orosomucoid, the lymphocyte activation was found in randomly selected blood donors which included normal healthy volunteers and patients with T cell immunodeficiency or Alzheimer's disease, demonstrating a consistent immunostimulatory action of this glycoprotein.     

Monocyte chemotaxis mediated by formyl-methionyl-leucyl-phenylalanine conjugated with monoclonal antibodies against human ovarian carcinoma

Availability of a chemically defined chemoattractant (fMLP) and of appropriate monoclonal antibodies may permit local manipulation of the inflammatory response to human tumors. fMLP has been conjugated with two monoclonal antibodies (OC125 and OC133) which react with human ovarian carcinomas. Conjugates retained the ability to bind to a human ovarian carcinoma line (OVCA433) judged by indirect immunofluorescence and by radioimmunoassay. The fMLP conjugate was maximally chemotactic for human blood monocytes and human peritoneal macrophages at protein concentrations of 300-900 micrograms/ml. Conjugates stimulated chemotaxis rather than chemokinesis. After incubation with an fMLP-antibody conjugate, antigen positive OVCA433 cells released chemotactic activity and attracted monocytes in vitro, whereas an antigen-negative ovarian cell line failed to do so. As monocytes can be important effectors of antibody dependent cell mediated cytoxicity, fMLP conjugates might increase monocyte concentrations at tumor sites and potentiate serotherapy for certain human neoplasms.