Antibody-dependent Cellular Cytotoxicity Capacity Research Articles

Comprehensive Exploration of NK Cell Education in ADCC Triggered By a Monoclonal Antibody or a Bispecific Killer Engager Molecule (BiKE)

The responsiveness of NK cells to malignant cells that lack self-HLA class I (HLA-I) expression is controlled by NK cell education governed by the interaction between selected inhibitory NK cell receptors and their cognate HLA-I ligands. However, it remains unclear to what extent education impacts the ability of NK cells to perform antibody-dependent cellular cytotoxicity (ADCC) as previous studies show inconsistent results and are limited in resolution. Moreover, no study has yet addressed if NK cell education impacts ADCC triggered by novel CD16-binding therapeutics such as bispecific killer engagers (BiKEs). In this study we systematically characterized NK cell degranulation against a panel of tumor cell lines with defined HLA-I expression in the presence of either the monoclonal antibody rituximab or a recently developed CD34xCD16 BiKE. Using high-resolution flow cytometry, our data revealed that NK cells educated by one or two KIRs did not have significantly enhanced ADCC capacity over uneducated KIR+ or KIR- NK cells, especially when increasing the antibody concentration. Contrasting co-education by KIRs, NKG2A was consistently associated with improved responsiveness and superior ADCC. Surprisingly, these results were despite that KIR-education correlated with higher CD16 expression that was markedly lower on NKG2A+ NK cells compared to both KIR-educated and uneducated subsets. An extended analysis uncovered that the inhibitory KIR2DL1-C245 receptor, reported to mediate weak NK cell education compared to the KIR2DL1-R245 variant, further repressed the ADCC capacity of NKG2A+ NK cells from donors expressing its ligand HLA C2. This highlights that also inhibitory KIRs can dampen the ADCC potential of NK cells similar to that of activating KIRs which also were discovered to restrict ADCC even when stimulated by its ligand. Finally, our study unveiled that BiKE-triggered ADCC has a similar relationship to NK cell education and its hierarchies as that triggered by a monoclonal antibody. In conclusion, the ADCC capacity of an NK cell is more regulated by restrictive mechanisms of education conferred by activating or selected inhibitory KIRs in individuals carrying the cognate KIR ligand than that of inhibitory KIRs conferring higher education potential. Hence, this study establishes that NK cell education does not enhance the ADCC capacity of an NK cell per se while providing new insights that also inhibitory KIRs can dampen the ADCC potential even when the target cell lacks its ligand. Our results add to the fundamental understanding of NK cell biology as well as to avenues of therapeutic applications for NK cells.

FcγR Binding and ADCC Activity of Human IgG Allotypes.

Antibody dependent cellular cytotoxicity (ADCC) is an Fc-dependent effector function of IgG important for anti-viral immunity and anti-tumor therapies. NK-cell mediated ADCC is mainly triggered by IgG-subclasses IgG1 and IgG3 through the IgG-Fc-receptor (FcγR) IIIa. Polymorphisms in the immunoglobulin gamma heavy chain gene likely form a layer of variation in the strength of the ADCC-response, but this has never been studied in detail. We produced all 27 known IgG allotypes and assessed FcγRIIIa binding and ADCC activity. While all IgG1, IgG2, and IgG4 allotypes behaved similarly within subclass, large allotype-specific variation was found for IgG3. ADCC capacity was affected by residues 291, 292, and 296 in the CH2 domain through altered affinity or avidity for FcγRIIIa. Furthermore, allotypic variation in hinge length affected ADCC, likely through altered proximity at the immunological synapse. Thus, these functional differences between IgG allotypes have important implications for therapeutic applications and susceptibility to infectious-, allo- or auto-immune diseases.

Chronic HIV-1 Infection Alters the Cellular Distribution of FcγRIIIa and the Functional Consequence of the FcγRIIIa-F158V Variant.

Chronic HIV-infection modulates the expression of Fc gamma receptors (FcγRs) on immune cells and their antibody-dependent effector function capability. Given the increasingly recognized importance of antibody-dependent cellular cytotoxicity (ADCC) in HIV-specific immunity, we investigated the cellular distribution of FcγRIIIa on cytotoxic lymphocytes—natural killer cells and CD8+ T cells—and the effect of the FcγRIIIa-F158V variant on ADCC capacity in HIV-infected individuals (n = 23) and healthy controls (n = 23). Study participants were matched for F158V genotypes, carried two copies of the FCGR3A gene and were negative for FcγRIIb expression on NK cells. The distribution of CD56dimFcγRIIIabright and CD56negFcγRIIIabright NK cell subsets, but not FcγRIIIa surface expression, differed significantly between HIV-1 negative and HIV-1 positive donors. NK cell-mediated ADCC responses negatively correlated with the proportion of the immunoregulatory CD56brightFcγRIIIadim/neg cells and were lower in the HIV-1 positive group. Intriguingly, the FcγRIIIa-F158V variant differentially affected the NK-mediated ADCC responses for HIV-1 negative and HIV-1 positive donors. Healthy donors bearing at least one 158V allele had higher ADCC responses compared to those homozygous for the 158F allele (48.1 vs. 34.1%), whereas the opposite was observed for the HIV-infected group (26.4 vs. 34.6%), although not statistically significantly different. Furthermore, FcγRIIIa+CD8bright and FcγRIIIa+CD8dim T cell subsets were observed in both HIV-1 negative and HIV-1 positive donors, with median proportions that were significantly higher in HIV-1 positive donors compared to healthy controls (15.7 vs. 8.3%; P = 0.016 and 18.2 vs. 14.1%; P = 0.038, respectively). Using an HIV-1-specific GranToxiLux assay, we demonstrate that CD8+ T cells mediate ADCC through the delivery of granzyme B, which was overall lower compared to that of autologous NK cells. In conclusion, our findings demonstrate that in the presence of an HIV-1 infection, the cellular distribution of FcγRIIIa is altered and that the functional consequence of FcγRIIIa variant is affected. Importantly, it underscores the need to characterize FcγR expression, cellular distribution and functional consequences of FcγR genetic variants within a specific environment or disease state.

Genetic variation of human neutrophil Fcγ receptors and SIRPα in antibody‐dependent cellular cytotoxicity towards cancer cells

The efficacy of cancer therapeutic antibodies varies considerably among patients. Anti-cancer antibodies act through different mechanisms, including antibody-dependent cellular cytotoxicity (ADCC) triggered via Fcγ receptors (FcγR). This phagocyte ADCC can be promoted by interference with CD47-SIRPα interactions, but the magnitude of this enhancement also varies among individuals. Both FcγR and SIRPα display considerable genetic variation, and we investigated whether this explains some of the variability in ADCC. Because of linkage disequilibrium between FcγR variants the interpretation of previous reports suggesting a potential link between FcγR polymorphisms and ADCC has been troublesome. We performed an integrated genetic analysis that enables stratification. ADCC by activated human neutrophils towards Trastuzumab-coated breast cancer cells was predominantly dependent on FcγRIIa. Neutrophils from individuals with the FcγRIIa-131H polymorphic variant displayed significantly higher killing capacity relative to those with FcγRIIa-131R. Furthermore, ADCC was consistently enhanced by targeting CD47-SIRPα interactions, and there were no significant functional differences between the two most prevalent SIRPα polymorphic variants. Thus, neutrophil ADCC capacity is directly related to the FcγRIIa polymorphism, and targeting CD47-SIRPα interactions enhances ADCC independently of FcγR and SIRPα genotype, thereby further suggesting that CD47-SIRPα interference might be a generic strategy for potentiating the efficacy of antibody therapy in cancer.

Lack of ADCC Breadth of Human Nonneutralizing Anti-HIV-1 Antibodies.

Anti-human immunodeficiency virus type 1 (HIV-1) nonneutralizing antibodies (nnAbs) capable of antibody-dependent cellular cytotoxicity (ADCC) have been identified as a protective immune correlate in the RV144 vaccine efficacy trial. Broadly neutralizing antibodies (bNAbs) also mediate ADCC in cell culture and rely on their Fc region for optimal efficacy in animal models. Here, we selected 9 monoclonal nnAbs and 5 potent bNAbs targeting various epitopes and conformations of the gp120/41 complex and analyzed the potency of the two types of antibodies to bind and eliminate HIV-1-infected cells in culture. Regardless of their neutralizing activity, most of the selected antibodies recognized and killed cells infected with two laboratory-adapted HIV-1 strains. Some nnAbs also bound bystander cells that may have captured viral proteins. However, in contrast to the bNAbs, the nnAbs bound poorly to reactivated infected cells from 8 HIV-positive individuals and did not mediate effective ADCC against these cells. The nnAbs also inefficiently recognize cells infected with 8 different transmitted-founder (T/F) isolates. The addition of a synthetic CD4 mimetic enhanced the binding and killing efficacy of some of the nnAbs in an epitope-dependent manner without reaching the levels achieved by the most potent bNAbs. Overall, our data reveal important qualitative and quantitative differences between nnAbs and bNAbs in their ADCC capacity and strongly suggest that the breadth of recognition of HIV-1 by nnAbs is narrow.IMPORTANCE Most of the anti-HIV antibodies generated by infected individuals do not display potent neutralizing activities. These nonneutralizing antibodies (nnAbs) with antibody-dependent cellular cytotoxicity (ADCC) have been identified as a protective immune correlate in the RV144 vaccine efficacy trial. However, in primate models, the nnAbs do not protect against simian-human immunodeficiency virus (SHIV) acquisition. Thus, the role of nnAbs with ADCC activity in protection from infection remains debatable. In contrast, broadly neutralizing antibodies (bNAbs) neutralize a large array of viral strains and mediate ADCC in cell culture. We analyzed the capacities of 9 nnAbs and 5 bNAbs to eliminate infected cells. We selected 18 HIV-1 strains, including virus reactivated from the reservoir of HIV-positive individuals and transmitted-founder isolates. We report that the nnAbs bind poorly to cells infected with primary HIV-1 strains and do not mediate potent ADCC. Overall, our data show that the breadth of recognition of HIV-1 by nnAbs is narrow.

Asymmetrical Fc Engineering Greatly Enhances Antibody-dependent Cellular Cytotoxicity (ADCC) Effector Function and Stability of the Modified Antibodies

Antibody-dependent cellular cytotoxicity (ADCC) is mediated through the engagement of the Fc segment of antibodies with Fcγ receptors (FcγRs) on immune cells upon binding of tumor or viral antigen. The co-crystal structure of FcγRIII in complex with Fc revealed that Fc binds to FcγRIII asymmetrically with two Fc chains contacting separate regions of the FcγRIII by utilizing different residues. To fully explore this asymmetrical nature of the Fc-FcγR interaction, we screened more than 9,000 individual clones in Fc heterodimer format in which different mutations were introduced at the same position of two Fc chains using a high throughput competition AlphaLISA® assay. To this end, we have identified a panel of novel Fc variants with significant binding improvement to FcγRIIIA (both Phe-158 and Val-158 allotypes), increased ADCC activity in vitro, and strong tumor growth inhibition in mice xenograft human tumor models. Compared with previously identified Fc variants in conventional IgG format, Fc heterodimers with asymmetrical mutations can achieve similar or superior potency in ADCC-mediated tumor cell killing and demonstrate improved stability in the CH2 domain. Fc heterodimers also allow more selectivity toward activating FcγRIIA than inhibitory FcγRIIB. Afucosylation of Fc variants further increases the affinity of Fc to FcγRIIIA, leading to much higher ADCC activity. The discovery of these Fc variants will potentially open up new opportunities of building the next generation of therapeutic antibodies with enhanced ADCC effector function for the treatment of cancers and infectious diseases.

Effectiveness of drainage improvements in reducing sediment production rates from an unpaved road

Cultured human monocytes undergo a process of differentiation and maturation lasting 5 to 10 days that ultimately leads to the appearance of large macrophage-like cells. This differentiation is growth factor dependent: of all the cytokines tested, only macrophage colony-stimulating factor (M-CSF), granulocyte/macrophage-CSF (GM-CSF), and IL-3 proved capable of supporting the differentiation and the long term survival of the macrophage-like cells. Although all three cytokines yield cells with macrophage characteristics, cells developed in M-CSF have features distinct from those matured in either IL-3 or GM-CSF. At the morphologic level, the M-CSF-supported monocyte cultures yield elongated, spindle-shaped cells whereas those supported with IL-3 or GM-CSF yielded round cells with distinct nuclei. All three macrophage populations expressed similar levels of HLA-DR, CD11b, and CD11c, but the M-CSF-treated cultures yielded more CD14+ and CD16+ (Fc gamma RIII) cells. All three cell populations developed capacity for antibody-dependent cellular cytotoxicity (ADCC) as well as antibody-independent cytotoxicity with peak activity achieved after 8 to 12 days in culture. ADCC capacity developed earliest and the level of activity was usually greatest in the M-CSF-treated cultures, possibly correlating with the higher level of expression of CD16. Our findings indicate that any of these cytokines, but particularly M-CSF, may be useful clinically in enhancing the tumoricidal capacity of tumor-specific mAb through augmentation of macrophage capacity for ADCC.

Diminished Response to Interleukin-10 and Reduced Antibody-Dependent Cellular Cytotoxicity of Cord Blood Monocyte-Derived Macrophages

Monocyte-derived macrophage (MPhi) subsets are generated by antagonistic induction pathways. A helper MPhi-type (Mh-MPhi) is induced by interferon gamma (IFN-gamma), whereas a cytotoxic MPhi-type (Mc-MPhi), induced by interleukin-10 (IL-10), is a potent mediator of antibody-dependent cellular cytotoxicity (ADCC). Compared with MPhi from healthy adults [peripheral blood monocyte-derived macrophages (PBMPhi)], cord blood MPhi (CBMPhi) were found less capable of generating Mh-MPhi. Here we tested the hypothesis that their generation of Mc-MPhi via IL-10 is also impaired. MPhi surface markers were phenotyped. IL-10 protein and mRNA production were detected after stimulation [alphaCD3 monoclonal antibody (mAb)]. CBMPhi or PBMPhi were co-cultured with MPhi-depleted mononuclear cells of adults and CD4-targeting antibodies as models for ADCC were added. In cord blood, we found diminished alphaCD3-induced IL-10 protein and mRNA production (p < 0.05 versus adults). Basal CD16 and HLA-DR expressions on CBMPhi of preterm and full-term neonates were lower (p < 0.05 versus PBMPhi). IL-10 had reduced effects on CD16 up- and HLA-DR down-modulation on CBMPhi (p < 0.05 versus PBMPhi). CD4-directed receptor modulation and deletion were reduced in the presence of CBMPhi (p < 0.05 versus PBMPhi). IL-10 failed to enhance their ADCC capacity, which was in contrast to PBMPhi (p < 0.05). These data suggest that CBMPhi have an impaired cytotoxic capacity via lower sensitivity toward IL-10.

Prestimulation of monocytes by the cytokines GM-CSF or IL-2 enhances the antibody dependent cellular cytotoxicity of monoclonal antibody 17-1A.

Previously, we have shown that the cytokines IFN-alpha, IFN-gamma and IL-2 significantly enhance the antibody dependent cellular cytotoxicity (ADCC) exerted by the monoclonal antibody (mAb) 17-1A which recognizes the tumor associated antigen EpCAM. ADCC was assessed by a new flow cytometric cytotoxicity assay using the PKH2 labeled colorectal tumor cell line HT29 as target cells and peripheral blood mononuclear cells as effectors. Monocytes are assumed to be one of the major effectors for ADCC. However, isolated monocytes have a rather low ADCC capacity while addition of CD4+ lymphocytes optimizes ADCC. Since such an interaction between immune cells may act through cytokines we investigated whether a seven-day-prestimulation of monocytes by the cytokines M-CSF, GM-CSF, IFN-gamma, IFN-alpha and IL-2 enhances ADCC. Thereafter, we added for three days IL-2 and IFN-alpha with or without the mAb 17-1A for terminal activation of monocytes. Interestingly, GM-CSF which was ineffective in terminal activation, significantly enhanced ADCC of monocytes when it was used for prestimulation. Similar results were obtained with IL-2. IFN-gamma and M-CSF were also active but less than GM-CSF. Astonishingly, IFN-gamma and IFN-alpha prestimulation of monocytes suppressed the enhancement of ADCC exerted by GM-CSF and IL-2, respectively. Our experiments suggest that the timing of cytokine application is critical for the induction of optimal ADCC. Subcutaneous pretreatment with GM-CSF or IL-2 followed by the combination of IL-2/IFN-alpha/17-1A should be evaluated in a phase I clinical trial in patients with colorectal cancer.

Influence of physical activity stress and age on the ADCC of lymphocytes from mice

The influence of physical activity stress (swimming until exhaustion) and age on the antibody-dependent cellular cytotoxicity (ADCC) of lymphocytes from spleen, thymus and axillary lymph nodes in BALB/c mice was studied. The results indicate that the ADCC activity decreases after the acute stress both in young and in old mice. However, when swimming until exhaustion is performed after 1 month training, the ADCC activity increases except in the case of spleen lymphocytes from old mice. The basal ADCC capacity of spleen lymphocytes from old controls is higher ( P < 0.05) than from young controls, but there are no statistically significant differences in this respect between young and old animals in lymphocytes from thymus and axillary lymph nodes. No correlations between the increase in serum corticosterone levels and ADCC response are found.

Comparison of the effects of IL-3, granulocyte-macrophage colony-stimulating factor, and macrophage colony-stimulating factor in supporting monocyte differentiation in culture. Analysis of macrophage antibody-dependent cellular cytotoxicity.

Cultured human monocytes undergo a process of differentiation and maturation lasting 5 to 10 days that ultimately leads to the appearance of large macrophage-like cells. This differentiation is growth factor dependent: of all the cytokines tested, only macrophage colony-stimulating factor (M-CSF), granulocyte/macrophage-CSF (GM-CSF), and IL-3 proved capable of supporting the differentiation and the long term survival of the macrophage-like cells. Although all three cytokines yield cells with macrophage characteristics, cells developed in M-CSF have features distinct from those matured in either IL-3 or GM-CSF. At the morphologic level, the M-CSF-supported monocyte cultures yield elongated, spindle-shaped cells whereas those supported with IL-3 or GM-CSF yielded round cells with distinct nuclei. All three macrophage populations expressed similar levels of HLA-DR, CD11b, and CD11c, but the M-CSF-treated cultures yielded more CD14+ and CD16+ (Fc gamma RIII) cells. All three cell populations developed capacity for antibody-dependent cellular cytotoxicity (ADCC) as well as antibody-independent cytotoxicity with peak activity achieved after 8 to 12 days in culture. ADCC capacity developed earliest and the level of activity was usually greatest in the M-CSF-treated cultures, possibly correlating with the higher level of expression of CD16. Our findings indicate that any of these cytokines, but particularly M-CSF, may be useful clinically in enhancing the tumoricidal capacity of tumor-specific mAb through augmentation of macrophage capacity for ADCC.

Reduced antibody-dependent cellular cytotoxicity to herpes simplex virus-infected cells of salivary polymorphonuclear leukocytes and inhibition of peripheral blood polymorphonuclear leukocyte cytotoxicity by saliva.

Blood polymorphonuclear leukocytes (BPMN) have been shown to mediate antibody-dependent cellular cytotoxicity (ADCC) against HSV-infected cells. Although HSV infections are frequently found in the oral cavity, the ADCC capacity of salivary PMN (SPMN) has not been studied, mainly because methods to isolate SPMN were not available. We have recently developed a method to isolate SPMN, and in this study have evaluated their ADCC activity against HSV-infected cells. SPMN were obtained by repeated washings of the oral cavity, and separated from epithelial cells by nylon mesh filtration. ADCC was quantitatively determined by 51Cr release from HSV-infected Chang liver cells. SPMN in the presence of antibody were able to destroy HSV-infected cells, but SPMN were much less effective in mediating ADCC than BPMN (3.4% vs 40.7%, p less than 0.0001). In the presence of antiviral antibody, SPMN were able to adhere to HSV-infected cells, but less so than BPMN (34% vs 67%), and specific antibody-induced adherence was significantly lower in SPMN (p less than 0.04). The spontaneous adherence to HSV-infected cells was higher for SPMN than BPMN. SPMN demonstrated up-regulation of the adhesion glycoprotein CD18, but down-regulation of the FcRIII receptor. Incubation with saliva decreased ADCC capacity of BPMN, up-regulated CD18 expression, and down-regulated FcRIII expression.

Macrophage colony-stimulating factor enhances monocyte and macrophage antibody-dependent cell-mediated cytotoxicity

In vitro culture of either human peripheral blood monocytes or murine peritoneal macrophages for 72 hr in the presence of macrophage colony-stimulating factor (M-CSF) dramatically increased their subsequent ability to mediate antibody-dependent cellular cytotoxicity (ADCC). The M-CSF-treated cells were more effective in ADCC at lower effector to target cell ratios and in the presence of lower concentrations of tumor-specific monoclonal antibody than the untreated control cells. Two other hematopoietic cytokines, granulocyte-macrophage colonystimulating factor and interleukin-3, reported to enhance other macrophage effector functions were ineffective in promoting the development of ADCC by cultured human monocytes. All three hematopoietic growth factors were capable of enhancing the ability of the cultured monocytes to secrete TNFα; however, TNFα is unlikely to be an important cytotoxic factor in ADCC because neutralizing antibodies against TNFα had no affect on ADCC in vitro. Further, much higher concentrations of M-CSF were required to augment monocyte TNFα release (20–100 ng/ml) than ADCC capacity (1–10 ng/ml). These results suggest that M-CSF administration might prove effective in increasing the tumoricidal activities of tumor-specific monoclonal antibodies by enhancing the capacity of monocytes and macrophages to mediate ADCC.

Opposite effects of amines on lymphocyte- and monocyte-mediated ADCC

The effect of different amines on antibody-dependent cellular cytotoxicity (ADCC) activity of human mononuclear cells was tested. Whereas monocyte cytotoxic capacity was significantly stimulated in the presence of methylamine (MA), dansylcadaverine (DC) and glycine ethylester (GEE), lymphocyte ADCC was markedly suppressed by these agents. The pharmacological actions of these compounds in our system are not related to their ability to inhibit transglutaminase (TGase) enzymes, since tertiary amines such as sarcosine ethylester (SEE) and chloroquine (CQ) elicited identical responses to MA, DC and GEE. The calmodulin (CAM) inhibitors trifluoperazine (TFP) and the more specific N- (6-aminohexyl)-5-chloro-1-naphtalene sulfonamide (W-7) [Hidaka, Sasaki, Tanaka, Endo, Ohno, Fujii & Nagata (1981) Proc. natn. Acad. Sci. U.S.A., 78, 4353–4357] mimicked the effects of amines on ADCC, suggesting the possibility that a CAM-regulated process might be involved in the functional changes provoked by amines on ADCC. Finally, binding of 125I-immune complexes to the effector cells in the presence of amines showed lack of correlation between alterations in ADCC capacity and FcγR expression.

Cinétique comparée de l'activité cytotoxique anticorps-dépendante à médiation cellulaire splénique de souris traitées par le BCG Ou Mycobacterium Smegmatis

Spleen cells from C3H/HeN mice treated with BCG or Mycobacterium smegmatis displayed similar increased antibody-dependent cellular cytotoxicity (ADCC) in vitro. This activity, which increased between the tenth and the thirty-first day after stimulation, reached twice the amount of ADCC activity developed by the control spleen cells. C3H/HeN mice treated with a complete adjuvant including M. smegmatis and squalane displayed a lower increase in their ADCC capacity (30% instead of 100%). Les cellules spléniques de souris C3H/HeN traitées par Mycobacterium smegmatis selon différents protocoles ont une activité ADCC (CCDA) (cytotoxicité anticorps-dépendante à médiation cellulaire) accure envers des globules rouges de poussin, selon une cinétique identique et dans des proportions semblables à celles observées au cours d'un traitement par le BCG. Ces résultats peuvent être rapprochés de l'effet antitumoral exercé in vivo par ces deux immunostimulants.

The ADCC capacity of macrophages from C3H/HeJ and A/J mice can be augmented by BCG.

Macrophages elicited from the peritoneal cavity of C3H/HejJ and A/J mice by bacillus Calmette-Guérin (BCG), although ineffective in mediating tumor cytotoxicity, had augmented capacity to mediate antibody-dependent cellular cytotoxicity (ADCC) against both erythroid and neoplastic target cells. The level of augmented ADCC was comparable to that expressed by BCG-activated macrophages from control C3H/HeN mice. The data suggest that the defective potential for cytolytic activation in 2 genetically deficient strains of inbred mice does not extend to augmentation of capacity for mediating ADCC and that full expression of cytolytic activation is not necessary for expression of augmented cytolysis of antibody-coated targets.

Characterization of a human macrophage-like cell line stimulated in vitro: a model of macrophage functions.

Abstract When cells of human macrophage-like cell line U937 are cultured in the presence of medium conditioned by mixed lymphocyte culture (MLC), PHA- or Con A-stimulated lymphocytes they demonstrate morphologic and functional characteristics of stimulation. The cells become larger, their surface more villous, and the cytoplasm has increased numbers of lysosomes and phagosomes. There is a marked (at least 10-fold) increase in antibody-dependent cellular cytotoxicity (ADCC) against both erythroid and tumor targets accompanied by increased expression of Fc receptors (FcR). There is also an augmentation of antibody-dependent phagocytosis. Medium conditioned by unstimulated lymphocytes, a B lymphoblastoid cell line or a fibroblast cell line produce very little stimulation of U937 cells. U937 cells gradually lose their increased ADCC capacity if they are washed free of conditioned medium (CM) but can be maintained in a stimulated state for long periods of time by culturing them in medium supplemented with PHA-CM at a concentration of 2%. Stimulation of macrophage-like cell line U937 may provide a useful model for further study of mechanisms of macrophage cytotoxicity and its modulation by products of activated lymphocytes.

Monocyte Function in Rheumatoid Arthritis

Monocytes derived from peripheral blood of patients with rheumatoid arthritis (RA) had a marked defect in their bactericidal activity against Staphylococcus albus and Listeria monocytogenes; whereas the phagocytic capacity of monocytes from RA patients for both Staph. albus and Shigella flexneri was similar to that of monocytes from healthy subjects. There were no significant differences between the patient and control groups with regard to antibody dependent cellular cytotoxicity (ADCC) of monocyte against antibody-coated EL4 leukemia tumor cells. No correlation was observed between the rheumatoid factor (RF) titer in the serum of RA patients and the ADCC capacity of their monocytes. The ADCC of normal monocytes was reduced markedly following their incubation with serum from RA patients. It suggested that the defect in bactericidal activity in monocytes from RA patients may explain, at least in part, the susceptibility of RA patients to infections.

Monocyte Function in Rheumatoid Arthritis

Monocytes derived from peripheral blood of patients with rehumatoid arthritis (RA) had a marked defect in their bactericidal activity against Staphylococcus al-bus and Listeria monocytogenes; whereas the phagocytic capacity of monocytes from RA patients for both Staph. albus and Shigella flexneri was similar to that of monocytes from healthy subjects. There were no significant differences between the patient and control groups with regard to antibody dependent cellular cytotoxicity (ADCC) of monocyte against antibody-coated EL4 leukemia tumor cells. No correlation was observed between the rheumatoid factor (RF) liter in the serum of RA patients and the ADCC capacity of their monocytes. The ADCC of normal monocytes was reduced markedly following their incubation with serum from RA patients. It suggested that the defect in bactericidal activity in monocytes from RA patients may explain, at least in part, the susceptibility of RA patients to infections.

Antibody-dependent cellular cytotoxicity of mononuclear cells from asthmatics tested in three in vitro assays

Using the chicken red blood cell assay, the human Chang liver cell assay, and a lymphoblastoid cell assay, mononuclear cells from asthmatics and normals were tested for antibody-dependent cellular cytotoxicity (ADCC) capacity. Mononuclear cell preparations from perennial nonallergic asthmatics with a history of asthma associated with viral infections had a reduced ADCC capacity in the chicken red blood cell assay, an increased ADCC capacity in the Chang liver cell assay, and normal ADCC capacity in the lymphoblastoid cell assay. The data also suggested that perennial nonallergic asthmatics had increased percentages of surface IgG-negative lymphocytes in the peripheral blood when compared to normals.