Association of a coding polymorphism in Fc gamma receptor 2A and graft survival in re-transplant candidates

The family of Fc gamma receptors (FcγRs) is involved in mediating immunological effector functions. FcγRs are differentially expressed on immune cells and can act either activating or inhibitory, with FcγR2A belonging to the first group. The polymorphism H131R (rs1801274) in FCGR2A has been associated with acute rejection and can shift the overall balance between activating and inhibitory FcγRs. Anti-HLA allo-antibodies in transplant recipients have been identified as risk factor for organ survival after transplantation. In this study we genotyped FCGR2A H131R in 200 patients who had undergone kidney transplantation and experienced loss of graft function. FCGR2A polymorphism was related to graft survival and anti-HLA antibodies. Graft survival was calculated as the time interval between transplantation and return to chronic dialysis after transplantation. The gene frequency of FCGR2A R/R131 was found significantly more often in patients with earlier (⩽60 months) compared to patients with later (>60 months) graft failure. Overall patients homozygous for R/R131 had a significantly shorter graft survival, compared to H/H131 or H/R131 which is even more pronounced, when anti-HLA antibodies were present. These data suggest, that FCGR2A polymorphisms constitute a risk factor for graft loss following kidney transplantation and that this effect is related to anti-HLA antibodies.     

Polymorphism of FCGR3A gene in sarcoidosis

We showed increased level of immune complexes (ICs) with mycobacterial heat shock proteins (Mtb-hsp) and increased expression of receptors for Fc fragment of immunoglobulin G (FcγR) I–III on blood monocytes with their increased phagocytic activity, responsible for clearance of these ICs in sarcoidosis (SA). Since FcγRIIIa is the most crucial in this process, we genotyped 77 SA patients and 143 healthy controls with polymerase chain reaction for V158F polymorphism of FCGR3A gene, encoding FcγRIIIa. We revealed significantly higher percentage of 158F and 158FF and lower of 158FV variants in Stage I of SA versus controls. Conversely, in Stage II of SA, we found increase in 158VV homozygotes versus controls. We also showed significant increase of 158F and 158FF variants in Stage I vs II and of 158V in Stage II vs I. Therefore, in Stage I, 158F allele may cause decreased FcγRIIIa affinity and clearance of ICs, whereas in Stage II, 158V allele may cause effective FcγRIIIa affinity to ICs with e.g. mycobacteria, their phagocytosis, Mtb-hsp secretion with ICs formation, Mtb-hsp epitope spread and subsequent immune reaction. Thus, V158F polymorphism of FCGR3A may explain the immunocomplexemia in our patients and might serve as prognostic marker of clinical course of sarcoidosis.     

Associations between FCGR polymorphisms and immune thrombocytopenia: A meta‐analysis

Several studies already explored associations between Fc gamma receptor (FCGR) polymorphisms and immune thrombocytopenia (ITP), but the results of these studies were not consistent. Consequently, we conducted a meta‐analysis of relevant studies to better analyse the effects of FCGR polymorphisms on individual susceptibility to ITP. PubMed, Web of Science, Embase and CNKI were searched for eligible studies. Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated. Totally 17 studies were eligible for analyses (1200 cases and 1723 controls). Significant associations with ITP were observed for FCGR3A F158V polymorphism in dominant (P < 0.0001, OR = 0.47, 95% CI 0.39‐0.57), recessive (P < 0.0001, OR = 2.03, 95% CI 1.58‐2.61), overdominant (P < 0.0001, OR = 1.42, 95% CI 1.19‐1.69) and allele (P < 0.0001, OR = 0.58, 95% CI 0.51‐0.65) models in overall analyses. But we did not observe any significant associations with ITP for FCGR2A H131R and FCGR2B I232T polymorphisms in overall analyses. Subgroup analyses by ethnicity yielded similar positive results for FCGR3A F158V polymorphism in both Asians and Caucasians. Furthermore, subgroup analyses by type of disease revealed that FCGR2A H131R polymorphism was significantly associated with childhood‐onset ITP, and FCGR3A F158V polymorphism was significantly associated with both childhood‐onset and adult‐onset ITP. In summary, our findings suggested that FCGR2A H131R polymorphism may serve as a potential genetic biomarker of childhood‐onset ITP, while FCGR3A F158V polymorphism may serve as a potential genetic biomarker of both childhood‐onset and adult‐onset ITP.     

High-affinity FcγRIIIa genetic variants and potent NK cell-mediated antibody-dependent cellular cytotoxicity (ADCC) responses contributing to severe COVID-19

PurposeHost genetic variants in activating natural killer (NK) cell receptors may contribute to differences in severity of COVID-19. NK cell-mediated antibody-mediated cellular cytotoxicity (ADCC) responses play, however, a controversial role in SARS-CoV-2 infections. It is unclear whether proinflammatory and cytotoxic SARS-CoV-2-specific ADCC responses limit disease severity or rather contribute to the immunopathogenesis of severe COVID-19.MethodsUsing a genetic association approach and subsequent in vitro antibody-dependent NK cell activation experiments, we investigated whether genetic variants in the FcγRIIIa-encoding FCGR3A gene, resulting in expression of either a low-affinity or high-affinity variant, and individual SARS-CoV-2-specific ADCC response contribute to COVID-19 severity.ResultsIn our study, we showed that the high-affinity variant of the FcγRIIIa receptor, 158-V/V, is significantly over-represented in hospitalized and deceased patients with COVID-19, whereas the low-affinity FcγRIIIa-158-F/F variant occurs more frequently in patients with mild COVID-19 (P < .0001). Furthermore, functional SARS-CoV-2 antibody-specific NK cell-mediated ADCC assays revealed that significantly higher proinflammatory ADCC responses occur in hospitalized patients with COVID-19, and are especially observed in NK cells expressing the FcγRIIIa-158-V/V variant (P < .0001).ConclusionOur study provides evidence that pronounced SARS-CoV-2-specific NK cell-mediated ADCC responses are influenced by NK cell FcγRIIIa genetic variants and are a hallmark of severe COVID-19.     

A novel FCGR3A intragenic haplotype is associated with increased FcγRIIIa/CD16a cell surface density and population differences

FcγRIIIa (CD16a) cell surface density affects immune complex binding and initiation of effector mechanisms. Investigations into the clinical relevance of variable FcγRIIIa surface density require baseline data from healthy individuals. In this study, proportions of FcγRIIIa-positive leukocyte subsets and corresponding FcγRIIIa cell surface densities were determined in whole blood from 53 healthy individuals (22 Black individuals, 31 Caucasians). Compared to Caucasians, Black individuals had significantly lower proportions of FcγRIIIa-positive natural killer (NK) cells (95.2% vs. 96.9%) and CD8⁺ T lymphocytes (9.6% vs. 11.7%), whereas the opposite was true for monocytes (24.2% vs. 16.3%). However, Black individuals had significantly lower FcγRIIIa surface densities on monocytes and NK cells compared to Caucasians (P < 0.001). We investigated FCGR3A gene copy number and novel polymorphisms, obtained from full gene sequencing, in relation to FcγRIIIa expression levels on NK cells. The broad range of FcγRIIIa surface densities was not attributed to variable FCGR3A gene copy number (all individuals had 2 gene copies except for 2/53 (3.8%) with one extra copy). However, a novel 3-SNP/1-indel FCGR3A intragenic haplotype may account for the significantly increased FcγRIIIa surface densities (P < 0.0001) and may explain the population differences. This genetic determinant may serve as predictive marker for a high-expressing FcγRIIIa phenotype.     

Fcγ receptor expression on splenic macrophages in adult immune thrombocytopenia

Splenic macrophages play a key role in immune thrombocytopenia (ITP) pathogenesis by clearing opsonized platelets. Fcγ receptors (FcγR) participate in this phenomenon, but their expression on splenic macrophages and their modulation by treatment have scarcely been studied in human ITP. We aimed to compare the phenotype and function of splenic macrophages between six controls and 24 ITP patients and between ITP patients according to the treatments they received prior to splenectomy. CD86, human leucocyte antigen D‐related (HLA‐DR) and FcγR expression were measured by flow cytometry on splenic macrophages. The major FcγR polymorphisms were determined and splenic macrophage function was assessed by a phagocytosis assay. The expression of the activation markers CD86 and HLA‐DR was higher on splenic macrophages during ITP compared to controls. While the expression of FcγR was not different between ITP and controls, the phagocytic function of splenic macrophages was reduced in ITP patients treated with intravenous immunoglobulin (IVIg) within the 2 weeks prior to splenectomy. The FCGR3A (158V/F) polymorphism, known to increase the affinity of FcγRIII to IgG, was over‐represented in ITP patients. Thus, these are the first results arguing for the fact that the therapeutic use of IVIg during human chronic ITP does not modulate FcγR expression on splenic macrophages but decreases their phagocytic capabilities.     

Study of common functional genetic polymorphisms of FCGR2A, 3A and 3B genes and the risk for cryptococcosis in HIV-uninfected patients.

A pilot candidate gene association study was conducted to investigate the role of three common functional genetic polymorphisms of the low-affinity Fc gamma receptors, FCGR2A (131H/R), FCGR3A (158F/V) and FCGR3B (NA1/NA2) in Cryptococcus neoformans infections in individuals not infected with HIV. The FCGR2A 131RR and FCGR3A 158VV genotypes were over-represented [OR: 1.67 (1.05-2.63) and 2.04 (1.06-4.00), respectively] whereas the FCGR3B NA2NA2 was under-represented in patients with cryptococcosis (28% vs. 40% in controls). An analysis of haplotypes showed a significant difference in distribution between cases and controls overall and in Caucasians.     

FcγRIIa and FcγRIIIb polymorphisms and associations with clinical manifestations in systemic lupus erythematosus patients

Abstract

In this study, we aimed to investigate whether the distribution of the FcγRIIa and FcγRIIIb polymorphisms determines susceptibility to systemic lupus erythematosus (SLE) and acts as predictors of SLE clinical manifestations in the Brazilian patients. A total of 157 patients that fulfilled the American College of Rheumatology classification criteria for SLE and 160 healthy volunteers were included in this study. FCGR2A and FCGR3B genotypes were determined by polymerase chain reaction-based allotyping methods with allele-specific primers; the clinical features were obtained from the patients' official medical records. In the case of FcγRIIa polymorphism, it was observed association of the allele FCGR2A-R-131 (p?=?0.02, odds ratio (OR)=1.44) and genotype RR-131 (p?=?0.03, OR?=?2.09) with SLE. These associations were higher with allele (p?<?0.01, OR?=?1.67) as well genotype (p?=?0.01, OR?=?2.85) when lupus nephritis was considered. In contrast, the allele FCGR2A-H-131 was associated with susceptibility to arthritis and anti-DNA antibodies (p?=?0.05 for both). As for FcγRIIIb polymorphism, skewing did not differ significantly between patients and controls, however the genotype FCGR3B*02*02 was associated with susceptibility to arthritis (p?=?0.02) and malar rash (p?=?0.03), but no association with nephritis was found. The results demonstrate that FcγRIIa polymorphism is associated with susceptibility to SLE in Brazilian patients, whereas for FcγRIIIb polymorphism no association was found. However, notably, both polymorphisms present allelic variants that influence the clinical manifestations and may contribute to the pathogenesis of the disease. In addition, to our knowledge, this is the first study considering the frequency of FcγRIIIb polymorphism in Brazilian SLE patients.     

Genetic variations in low-to-medium-affinity Fcγ receptors and autoimmune neutropenia in early childhood in a Danish cohort

Autoimmune neutropenia (AIN) in early childhood is caused by autoantibodies directed against antigens on the neutrophil membrane and is a frequent cause of neutropenia in children. Association of AIN with Fcγ receptor (FCGR) 3B variants is well described. In this study, we investigate genetic variations in the FCGR locus and copy number variation of FCGR3B. A total of 130 antibody-positive AIN patients, 64 with specific anti-HNA-1a antibodies and 66 with broad-reacting anti-FcγRIIIb antibodies, were genotyped with a multiplex ligation probe assay and compared with healthy controls. Positive findings were confirmed with real-time q-PCR. We determined copy numbers of the FCGR2 and FCGR3 genes and the following SNPs: FCGR2A Q62W (rs201218628), FCGR2A H166R (rs1801274), FCGR2B I232T (rs1050501), FCGR3A V176F (rs396991), haplotypes for FCGR2B/C promoters (rs3219018/rs780467580), FCGR2C STOP/ORF and HNA-1 genotypes in FCGR3B (rs447536, rs448740, rs52820103, rs428888 and rs2290834). Generally, associations were antibody specific, with all associations being representative of the anti-HNA-1a-positive group, while the only association found in the anti-FcγRIIIb group was with the HNA-1 genotype. An increased risk of AIN was observed for patients with one copy of FCGR3B; the HNA genotypes HNA-1a, HNA-1aa or HNA-1aac; the FCGR2A 166H and FCGR2B 232I variations; and no copies of FCGR2B 2B.4. A decreased risk was observed for HNA genotype HNA-1bb; FCGR2A 166R; FCGR2B 232T; and one copy of FCGR2B promoter 2B.4. We conclude that in our Danish cohort, there was a strong association between variation in the FCGR locus and AIN. The findings of different genetic associations between autoantibody groups could indicate the presence of two different disease entities and disease heterogeneity.     

中国汉族人群FcγRIIIA F158V基因多态性与系统性红斑狼疮及狼疮肾炎相关

目的研究中国汉族人群中,FcγRIIIA F158V单核苷酸多态性(SNPs)的分布,以及对系统性红斑狼疮(SLE)特别是狼疮肾炎(LN)的遗传易感性和病程变化等的影响。方法采用病例-对照研究,收集在北京协和医院就诊的324例SLE患者和相匹配的非自身免疫性疾病的319名健康志愿者和体检对照,利用多聚酶链式反应(PCR)、限制性片段长度多态性(RELP)以及DNA测序验证等技术检测FcγRIIIA F158V基因型。进一步结合临床资料进行统计分析。结果在中国汉族人群中,FcγRIIIA基因的F等位基因频率约为60.8%。FcγRIIIA基因多态性在SLE组和对照组之间存在显著差异,FF基因型的SLE患者出现LN的风险较高,而VV基因型的SLE患者出现早发LN的风险较低。结论 FcγRIIIA基因多态性与SLE的发病有关,FF纯合子基因型可能存在对LN的易感性。VV纯合子基因型可能对LN晚发存在一定保护作用。     

Copy number variation at the FCGR locus includes FCGR3A,FCGR2C and FCGR3B but not FCGR2A and FCGR2B

Human Fcã receptors (FcãRs) are glycoproteins that bind the Fc region of IgG. The genes encoding the low‐affinity FcãRs are located on chromosome 1q23‐24. Beside single nucleotide polymorphisms (SNPs), gene copy number variation (CNV) is now being recognized as an important indicator for inter‐individual differences. Recent studies on identifying CNV in the human genome suggest large areas at chromosome 1q23‐24 to be involved, and CNV in this region has been associated with manifestations of systemic autoimmune disease. To study both SNPs and CNV of the low‐affinity FcãRs in one assay, we have developed a Multiplex Ligation‐dependent Probe Amplification (MLPA) assay. A novel CNV for FCGR3A was observed. Similar to FCGR3B and FCGR2C, a gene‐dosage effect of FCGR3A was found, that seemed to correlate nicely with the FcãRIIIa expression on NK cells. Next, we delineated the approximate boundaries of CNV at the FCGR locus. Variation in co‐segregation of neighboring FCGR genes was limited to four variants, with patterns of Mendelian inheritance. No CNV of the FCGR2A and FCGR2B genes was observed in over 600 individuals. In conclusion, we report a novel CNV of the FCGR3A gene that correlates with FcãRIIIa expression and function on NK cells. Only FCGR3A, FCGR2C and FCGR3B show CNV, in contrast to FCGR2A and FCGR2B. © 2009 Wiley‐Liss, Inc.     

Human leukocyte antigen class-I variation is associated with atopic dermatitis: A case-control study

Atopic dermatitis (AD) is a common immune-medicated skin disease. Previous studies have explored the relationship between Human Leukocyte Antigen (HLA) allelic variation and AD with conflicting results. The aim was to examine HLA Class I genetic variation, specifically peptide binding groove variation, and associations with AD. A case-control study was designed to evaluate HLA class I allelic variation and binding pocket polymorphisms, using next generation sequencing on 464 subjects with AD and 388 without AD. Logistic regression was used to evaluate associations with AD by estimating odds ratios (95% confidence intervals). Significant associations were noted with susceptibility to AD (B*53:01) and protection from AD (A*01:01, A*02:01, B*07:02 and C*07:02). Evaluation of polymorphic residues in Class I binding pockets revealed six amino acid residues conferring protection against AD: A9F (HLA-A, position 9, phenylalanine) [pocket B/C], A97I [pocket C/E], A152V [pocket E], A156R [pocket D/E], B163E [pocket A] and C116S [pocket F]. These findings demonstrate that specific HLA class I components are associated with susceptibility or protection from AD. Individual amino acid residues are relevant to protection from AD and set the foundation for evaluating potential HLA Class I molecules in complex with peptides/antigens that may initiate or interfere with T-cell responses.     

Comparability of Antibody-Mediated Cell Killing Activity Between a Proposed Biosimilar RTXM83 and the Originator Rituximab

Background

Biosimilars are described as biological products that resemble the structure of original biologic therapeutic products, with no clinically meaningful differences in terms of safety and effectiveness from the original. A wide range of biosimilars are under development or are already licensed in many countries. Biosimilars are earning acceptance and becoming a reality for immunotherapy treatments mainly based on the alternatives for the commercial anti-CD20 monoclonal antibody rituximab. The most important mechanism of action reported for this antibody is the induction of antibody-dependent cell cytotoxicity (ADCC), which is associated with the polymorphisms present at the 158 position in the IgG receptor FcγRIIIa.

Objective

The aim of the study was to validate the functional comparability between the proposed rituximab biosimilar RTXM83 and the original product. To achieve this we assessed the binding capacity and ADCC induction of this biosimilar, taking into account the different FcγRIIIa-158 polymorphisms.

Methods

Binding capacity was evaluated by flow cytometry using CD20 positive cells and a wide range of antibody concentrations. The FcγRIIIa-158 polymorphisms were analyzed by polymerase chain reaction (PCR) followed by allele-specific restriction enzyme digestion. ADCC was measured by a colorimetric lactate dehydrogenase-release assay, using effector cells from donors with different FcγRIIIa-158 polymorphisms.

Results

Binding capacity assay showed no differences between both products. Regarding ADCC, a similar relative potency was obtained between both antibodies, showing a higher response for the FcγRIIIa-158 valine/valine (V/V) polymorphism compared to the phenylalanine/phenylalanine (F/F), for both rituximab and RTXM83.

Conclusion

Our data strongly suggest the biocomparability between the proposed biosimilar and the originator rituximab, in antibody recognition and ADCC activity. Additionally, our results suggest that donors with the FcγRIIIa-158V/V polymorphism induce a higher ADCC response, as has been reported.

     

The natural killer cell-associated rs9916629-C allele is a novel genetic risk factor for fatal COVID-19

The severity of COVID-19 is associated with individual genetic host factors. Among these, genetic polymorphisms affecting natural killer (NK) cell responses, as variations in the HLA-E- (HLA-E*0101/0103), FcγRIIIa- (FcγRIIIa-158-F/V), and NKG2C- (KLRC2^wt/del) receptor, were associated with severe COVID-19. Recently, the rs9916629-C/T genetic polymorphism was identified that indirectly shape the human NK cell repertoire towards highly pro-inflammatory CD56^bright NK cells. We investigated whether the rs9916629-C/T variants alone and in comparison to the other risk factors are associated with a fatal course of COVID-19. We included 1042 hospitalized surviving and 159 nonsurviving COVID-19 patients as well as 1000 healthy controls. rs9916629-C/T variants were genotyped by TaqMan assays and were compared between the groups. The patients' age, comorbidities, HLA-E*0101/0103, FcγRIIIa-158-F/V, and KLRC2^wt/del variants were also determined. The presence of the rs9916629-C allele was a risk factor for severe and fatal COVID-19 (p < 0.0001), independent of the patients' age or comorbidities. Fatal COVID-19 was more frequent in younger patients (<69.85 years) carrying the FcγRIIIa-158-V/V (p < 0.006) and in older patients expressing the KLRC2^del variant (p < 0.003). Thus, patients with the rs9916629-C allele have a significantly increased risk for fatal COVID-19 and identification of the genetic variants may be used as prognostic marker for hospitalized COVID-19 patients.     

Confirmation of association of FCGR3B but not FCGR3A copy number with susceptibility to autoantibody positive rheumatoid arthritis

The FCGR locus encoding the low-affinity Fcγ receptors (FcγR) for immunoglobulin G has largely been missed by genome-wide association studies due to complications with structural variation and segmental duplication. Recently identified copy number variants (CNVs) affecting FCGR3A and FCGR3B have been linked to a number of autoimmune disorders. We have developed and validated a novel quantitative sequence variant assay in combination with an adapted paralogue ratio test to examine independent CNVs carrying FCGR3A and FCGR3B in rheumatoid arthritis (RA) compared with healthy volunteers (n = 1,115 and 654, respectively). Implementation of a robust statistical analysis framework (CNVtools) allowed for systematic batch effects and for the inherent uncertainty of copy number assignment, thus avoiding two major sources of false positive results. Evidence for association with neither duplications nor deletions of FCGR3A was found; however, in line with previous studies, there was evidence of overrepresentation of FCGR3B deletions in RA (odds ratio [OR] 1.50, P = 0.028), which was more apparent in rheumatoid factor positive disease (OR 1.61, P = 0.011). The level of FcγRIIIb, encoded by FCGR3B, expression on neutrophils was shown to correlate with gene copy number. Thus, our results may highlight an important role for neutrophils in the pathogenesis of RA, potentially through reduced FcγRIIIb-mediated immune complex clearance.     

Genetic risk factors for infection in patients with early rheumatoid arthritis

We analyzed clinical and genetic factors contributing to infections in 457 subjects with early rheumatoid arthritis (RA) enrolled in a prospective, 1-year clinical trial of methotrexate and the TNF inhibitor etanercept. Subjects were genotyped for the following single nucleotide polymorphisms (SNPs): (TNF -308, -238, and + 488); lymphotoxin-alpha (LTA) (LTA + 249, + 365, and + 720); and Fc gamma receptors FCGR2A 131 H/R; FCGR3A 176 F/V; and FCGR3B NA 1/2 and genotypes were correlated with infections. At least one URI was noted in 52% of subjects (99/191) with the NA2/NA2 genotype of the neutrophil-specific FCGR3B gene, compared to 42% (77/181) of those with the NA1/NA2 genotype and 39% (23/59) of those with the NA1/NA1 genotype (P = 0.038). Urinary tract infection (UTI) was associated with the TNF -238 A (odds ratio(OR) 2.56, 95% confidence interval (CI) 1.05-6.25) and LTA +365 C (OR 1.73, 95% CI 1.07-2.79) alleles, and marginally with the FCGR3A F allele (OR 1.72, 95% CI 0.99-3.00). There was a striking linear correlation between UTI and the number of risk alleles defined by these three SNPs (P < 0.001), suggesting an additive effect on susceptibility. These findings have important implications for the role of genetics in susceptibility to bacterial and viral infections.     

Genetic dissection of a major haplotype associated with arthritis reveal FcγR2b and FcγR3 to act additively

A haplotype with tightly linked Fc gamma receptor (FcγR) genes is known as a major locus controlling immune responses and autoimmune diseases, including arthritis. Here, we split a congenic fragment derived from the NOD mouse (Cia9) to study its effect on immune response and arthritis in mice. We found that arthritis susceptibility was indeed controlled by the FcγR gene cluster and a recombination between the Fc γ R2b and Fc γ R3 loci gave us the opportunity to separately study their impact. We identified the NOD-derived Fc γ R2b and Fc γ R3 alleles as disease-promoting for arthritis development without impact on antibody secretion. We further found that macrophage-mediated phagocytosis was directly correlated to Fc γ R3 expression in the congenic mice. In conclusion, we positioned Fc γ R2b and Fc γ R3 alleles as disease regulatory and showed that their genetic polymorphisms independently and additively control innate immune cell activation and arthritis.     

T lymphocyte development in the absence of Fcϵ receptor Iγ subunit: analysis of thymic-dependent and independent αβ and γδ pathways

During fetal development, early thymocyte progenitors transiently express low affinity Fc receptors for IgG (FcγR) of both FcγRII and III isoforms. Only the FcγRIII isoform requires association of an FcγRIII (CD16) α subunit with an FcϵRIγ homodimer for surface expression. To address the role of FcγR in ontogeny, we studied thymic development in FcϵRIγ^−/− mice. We find that day 14.5 CD4⁻CD8⁻ double-negative (DN) fetal thymocytes of FcϵRIγ^−/− mice express mRNA of both FcγRIIb₁ and FcγRIII. Surface expression of FcγRII/III is readily detected on these cells. It appears that FcγRIIb₁, whose surface expression is FcϵRIγ independent, replaces FcγRIII during thymic development in these animals. Moreover, subsequent development into CD4⁺CD8⁺ double-positive and CD4⁺CD8⁻ and CD4⁻CD8⁺ single-positive subsets appears normal even in the absence of FcϵRIγ. However, alterations were noted in adult animals among the DN αβ TCR⁺ thymocytes and peripheral splenic DN T cells as well as CD8αα⁺ intestinal intraepithelial lymphocytes (iIEL). In contrast to conventional T lymphocytes, which do not express either FcγRIII or FcϵRIγ, DN αβ TCR⁺ thymocytes and extrathymically derived αβ TCR⁺ and γδ TCR⁺ CD8αα⁺β⁻ iIEL express TCR which incorporate FcϵRIγ as one of their subunits. Consistent with this, the TCR levels of these cells are lower than the TCR levels on cells from wild-type C57BL/6 mice. Despite the reduction in the level of surface TCR, the development of these cells was unaltered by the absence of FcϵRIγ. Thus, we observed alterations in adult DN αβ TCR⁺ thymocytes, splenic DN αβ TCR⁺ and DN γδ TCR⁺ large granular lymphocytes (LGL), and αβ TCR⁺ and γδ TCR⁺ CD8αα⁺β⁻ iIEL, but no detectable changes in their major fetal thymic developmental pathways. Cultivation of peripheral DN αβ TCR⁺ and DN γδ TCR⁺ cells from FcϵRIγ^−/− mice with interleukin-2 generates LGL which mediate natural killer activity. Unlike LGL from wild-type C57BL/6 mice, LGL from FcϵRIγ^−/− mice lack FcγRIII expression and could not mediate antibody-dependent cellular cytotoxicity through FcγRIII.