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P J Capel

Publications and source records attributed to P J Capel.

At least 37 records · Page 2Linked to original sources
PubMed1995

Molecular basis for a familial defect in phagocyte expression of IgG receptor I (CD64).

Four individuals have been identified, within a single family, who lack phagocyte expression of the high affinity type I IgG receptor (CD64). As a result, their monocytes are unable to support mouse IgG2a anti-CD3-induced T cell mitogenesis (nonresponder individuals). Southern blotting proved all three human Fc gamma receptor I (hFc gamma RI) genes to be present in nonresponders without major structural changes. Nucleotide sequencing showed identical hFc gamma RIA promoter regions in all individuals. At the message level, a distinct difference was noted between monocytes from control (responder) donors and from nonresponders. Both a 1.7- and 1.6-kb message were found in responders, whereas in nonresponders only the 1.6-kb species was detectable. Reverse transcriptase-PCR analyses showed the hFc gamma RIa transcript (encoding a receptor with three extracellular Ig-like domains) to be present at a approximately 15- to 20-fold lower level in nonresponder monocytes. Importantly, we found a single nucleotide difference (C --> T) within the extracellular domain exon 1-encoding region of hFc gamma RIA in nonresponders, resulting in the change of codon 92 (encoding an arginine) into a termination codon. This change likely affects mRNA stability and, thereby, leads to undetectable expression of phagocyte-hFc gamma RIa. Despite this defect, these individuals are apparently healthy, suggesting that hFc gamma RIa is dispensable for phagocyte functioning.

Adult↗
PubMed1995

Skewed distribution of IgG Fc receptor IIa (CD32) polymorphism is associated with renal disease in systemic lupus erythematosus patients.

OBJECTIVE: Fc gamma receptors of class IIa (Fc gamma RIIa) occur in 2 allelic forms, with either a low (IIa-R131) or a high (IIa-H131) affinity for complexed IgG2 and IgG3. This polymorphism might have implications for the handling of immune complexes. Therefore, we determined the distribution of the Fc gamma RIIa allotypes in patients with systemic lupus erythematosus (SLE), with or without a history of lupus nephritis. METHODS: We studied 95 unrelated white European patients with SLE, as defined by the American College of Rheumatology criteria, 50 of whom had a history of lupus nephritis, and 69 healthy white European control subjects. Fc gamma RIIa allotypes were determined by immunophenotyping of blood monocytes. RESULTS: It was found that lupus nephritis was significantly associated with the "low affinity" Fc gamma RIIa R/R131 allotype and with the R131 allele, compared with healthy controls. No significant association was found upon comparison of groups with and without nephritis. CONCLUSION: SLE patients with a history of lupus nephritis have an abnormal distribution of Fc gamma RIIa allotypes. Fc gamma RIIa may well play a role in the pathogenesis of lupus nephritis, since IIa-R/R131 SLE patients seem to have a higher incidence of developing this complication.

Adult↗
PubMed1995

Human immunoglobulin G (IgG) Fc receptor IIA (CD32) polymorphism and IgG2-mediated bacterial phagocytosis by neutrophils.

Human immunoglobulin G (IgG) Fc receptor IIa (Fc gamma RIIa; CD32) is expressed on phagocytes, triggers phagocytosis, and represents the sole Fc receptor for IgG (Fc gamma R) capable of interaction with IgG2, the main IgG subclass induced in response to bacterial capsular polysaccharides. The two genetically determined structurally different allotypes of human Fc gamma RIIa, the products of the Fc gamma RIIa-R131 and IIa-H131 alleles, have functionally different reactivities with human IgG2. In humans, the Fc gamma RIIa-H131 allotype is known to interact efficiently with complexed human IgG2, whereas the IIa-H131 allotype does so only poorly. This polymorphism may therefore have implications for IgG2-mediated phagocytosis of encapsulated bacteria and susceptibility to bacterial infections. Phagocytosis of IgG2-opsonized bacteria by homozygous Fc gamma RIIa-R/R131, heterozygous IIa-H/R131, and homozygous IIa-H/H131 polymorphonuclear cells (PMN) was compared. A higher phagocytic capacity of IgG2-opsonized group B type III streptococci by PMN of homozygous H/H131 individuals compared with PMN from homozygous R/R131 individuals was observed (P = 0.001), while heterozygous IIa-H/R131 PMN showed intermediate phagocytosis. In this model system, IgG2-mediated phagocytosis was independent of the Fc gamma RIIIb-NA1/NA2 allelic polymorphism.

Antigens, CD↗
PubMed1994

Intra- and extracellular amyloid fibrils are formed in cultured pancreatic islets of transgenic mice expressing human islet amyloid polypeptide.

Islet amyloid polypeptide (IAPP) is the constituent peptide of amyloid deposits found in the islets of non-insulin-dependent diabetic patients. Formation of islet amyloid is associated with a progressive destruction of insulin-producing beta cells. Factors responsible for the conversion of IAPP into insoluble amyloid fibrils are unknown. Both the amino acid sequence of human IAPP (hIAPP) and hypersecretion of hIAPP have been implicated as factors for amyloid fibril formation in man. We have generated transgenic mice using rat insulin promoter-hIAPP or rat IAPP (rIAPP) gene constructs. No fibrillar islet amyloid was detectable in vivo in these normoglycemic mice, although small amorphous perivascular accumulations of IAPP were observed in hIAPP mice only. To determine the effects of glucose on IAPP secretion and fibrillogenesis, pancreatic islets from transgenic and control mice were examined in vitro. Islet IAPP secretion and content were increased in transgenic islets compared with control islets. IAPP-immunoreactive fibrils were formed at both intra- and extracellular sites in isolated hIAPP islets cultured with glucose at 11.1 and 28 mM for only 7 days. At 28 mM glucose, fibrils were present in deep invaginations of beta cells as observed in non-insulin-dependent diabetic patients. No fibrils were present at low glucose concentrations in hIAPP islets or at any glucose concentration in rIAPP or control islets. Thus, glucose-induced expression and secretion of hIAPP in transgenic mouse islets can lead to formation of amyloid fibrils similar to that found in non-insulin-dependent diabetes mellitus.

Amyloid↗
PubMed1994

Functional analysis of human Fc gamma RII (CD32) isoforms expressed in B lymphocytes.

The low affinity IgG receptor Fc gamma RII (CD32) represents the most widely distributed class of human Fc gamma R. To analyze the biologic functions of different Fc gamma RII isoforms, we stably transfected Fc gamma RIIb1, IIb1*, IIb2, IIa, and a IIa tail- mutant to the mouse IIA1.6 B lymphoma cell line. Of these, Fc gamma RIIb1* represents a receptor variant that is identical to IIb1 except for a single amino acid difference in the cytoplasmic tail (amino acid position 11) where a tyrosine (IIb1) is replaced by an aspartic acid (IIb1*). Evaluation of capping ability showed the Fc gamma RIIb1 molecules to cap effectively, which was even more apparent with IIb1*. None of the Fc gamma RIIa, IIa tail-, or IIb2 isoforms capped significantly. Internalization of Fc gamma R-antibody complexes proved very efficient for both the Fc gamma RIIa and IIb2 isoforms, whereas the IIb1 molecules internalized moderately compared with IIb1*, which internalized less efficiently. Notably, human IgG aggregates were internalized effectively by Fc gamma RIIa and moderately by IIb2. Neither Fc gamma RIIb1 nor IIb1* proved capable of internalizing such IgG aggregates. Cross-linking of the different Fc gamma R molecules showed Fc gamma RIIa capable of triggering increases in [Ca2+]i. Fc gamma R expressed on B cells were able to down-regulate [Ca2+]i on co-cross-linking with slgG. Notably, all three Fc gamma RIIb receptors proved active in this respect, in contrast to Fc gamma RIIa. The cell distribution of these Fc gamma RII isoforms was analyzed in a panel of human B cell lines to complement the IIA1.6 B cell model. Fc gamma RIIa was found expressed both at message and protein levels in all tested human B cell lines. In the pre-B cell lines evaluated, no Fc gamma RIIb molecules were detectable, whereas both Fc gamma RIIb1 and IIb2 molecules were found present in more mature B cell lines. These data support both a complex expression pattern of Fc gamma RII isoforms in B cell lines and functional differences between these B cell molecules.

B-Lymphocytes↗
PubMed1994

Antisense oligonucleotides, a novel tool for the control of cytokine effects on human cartilage. Focus on interleukins 1 and 6 and proteoglycan synthesis.

OBJECTIVE: To prevent the negative effects of interleukin-1 (IL-1) and IL-1-induced IL-6 on cartilage proteoglycan (PG) synthesis, we used an antisense oligonucleotide (ASO) specific for IL-6 messenger RNA (mRNA) to inhibit IL-6 production. METHODS: Explants of human articular cartilage were cultured in the presence or absence of IL-6-ASO, IL-1, and exogenous IL-6. As metabolic parameters, cartilage production of IL-6 was determined in the B9 bioassay and PG as incorporation of 35SO4. RESULTS: The IL-6-ASO prevented IL-1-induced production of IL-6 in the cartilage explants, as well as IL-1-induced inhibition of PG synthesis. This inhibition was restored, despite the presence of IL-6-ASO, when exogenous IL-6 was added. A control ASO (not specific for IL-6 mRNA) was not effective. CONCLUSION: The IL-6-ASO used can penetrate the extracellular matrix of articular cartilage, enter the chondrocytes, and inhibit the IL-1-induced production of IL-6. Furthermore, IL-6-ASO can prevent the IL-1-induced inhibition of cartilage PG synthesis. The effect of exogenous IL-6 shows that IL-1 requires IL-6 for inhibition of PG synthesis.

Aged↗
PubMed1994

Molecular physiology of the islet amyloid polypeptide (IAPP)/amylin gene in man, rat, and transgenic mice.

Islet amyloid polypeptide ("amylin") is the major protein component of amyloid deposits in pancreatic islets of type 2 (non-insulin-dependent) diabetic patients. Islet amyloid polypeptide consists of 37 amino acids, is co-produced and co-secreted with insulin from islet beta-cells, can act as a hormone in regulation of carbohydrate metabolism, and is implicated in the pathogenesis of islet amyloid formation and of type 2 diabetes mellitus. Rat islet amyloid polypeptide differs from human islet amyloid polypeptide particularly in the region of amino acids 25-28, which is important for amyloid fibril formation. In rat and mouse, diabetes-associated islet amyloid does not develop. To study the genetic organization and biosynthesis of islet amyloid polypeptide, we have isolated and analyzed the human and rat islet amyloid polypeptide gene and corresponding cDNAs. Both genes contain 3 exons, encoding precursor proteins of 89 amino acids and 93 amino acids, respectively. Apart from a putative signal sequence, these precursors contain amino- and carboxy-terminal flanking peptides in addition to the mature islet amyloid polypeptide. To understand regulation of islet amyloid polypeptide gene expression, we have identified several potential cis-acting transcriptional control elements that influence beta-cell-specific islet amyloid polypeptide gene expression. Using antisera raised against synthetic human islet amyloid polypeptide we developed a specific and sensitive radioimmunoassay to measure levels of islet amyloid polypeptide in plasma and tissue extracts. Also antisera raised against the flanking peptides will be used in studying human islet amyloid polypeptide biosynthesis. Elevated plasma islet amyloid polypeptide levels have been demonstrated in some diabetic, glucose-intolerant, and obese individuals, as well as in rodent models of diabetes and obesity. To examine the potential role of islet amyloid polypeptide overproduction in the pathogenesis of islet amyloid formation and type 2 diabetes, we generated transgenic mice that overproduce either the amyloidogenic human islet amyloid polypeptide or the nonamyloidogenic rat islet amyloid polypeptide in their islet beta-cells. Despite moderately to highly (up to 15-fold) elevated plasma islet amyloid polypeptide levels, no marked hyperglycemia, hyperinsulinemia or obesity was observed. This suggests that chronic overproduction of islet amyloid polypeptide "per se" does not cause insulin resistance. No islet amyloid deposits were detected in mice up to 63 weeks of age, but in every mouse producing human islet amyloid polypeptide (as in man), accumulation of islet amyloid polypeptide was observed in beta-cell lysosomal bodies. This may represent an initial phase in intracellular amyloid fibril formation.(ABSTRACT TRUNCATED AT 400 WORDS)

Amino Acid Sequence↗
PubMed1994

Heterogeneity of human IgG Fc receptors.

The complex family of human IgG Fc receptors show a wide cellular distribution and a strong functional heterogeneity. To date, eight different genes that are transcribed into at least 12 different mRNAs have been recognized. Although corresponding products have been identified for only some of the transcripts, in vivo at least six different Fc gamma R isoforms are shown to be present on the surface of all kinds of leukocytes. Upon interaction with immunoglobulin, Fc gamma R mediate a variety of biological responses such as phagocytosis, endocytosis, release of inflammatory mediators, and antibody-dependent cellular cytotoxicity. One of the main questions in Fc gamma R research is determining the specific relationship between a particular Fc gamma R isoform and a particular effector mechanism. The availability of the cDNA and genomic clones corresponding to the different isoforms, combined with different gene transfer systems in vitro and in vivo and the recently developed procedure of gene knockout by homologous recombination, allows the generation of stably transfected cell lines and transgenic animals that express one particular Fc gamma R isoform. These model systems enable us to study the function of a particular Fc gamma R isoform in the context of a particular cell type in vitro and in the context of the intact immune system in vivo.

Genes, Immunoglobulin↗
PubMed1994

Fc gamma receptor IIa (CD32) heterogeneity in patients with recurrent bacterial respiratory tract infections.

Fc gamma RIIa (CD32) is the sole IgG Fc receptor capable of interaction with human IgG2, the main IgG subclass of bacterial capsular polysaccharides. The two genetically determined allotypes of human Fc gamma RIIa, Fc gamma RIIa-R131 and IIa-H131 alleles, have functionally different reactivities with human IgG2. The capacity of polymorphonuclear leukocytes (PMNL) homozygous for Fc gamma RIIa-H/H131 for IgG2 opsonized bacteria is significantly higher than phagocytosis by PMNL homozygous for Fc gamma RIIa-R/R131, independent of the Fc gamma RIIb-NA1/NA2 (CD16) allelic polymorphism. To test the clinical significance of these Fc gamma R polymorphisms, Fc gamma RIIa and Fc gamma RIIIb phenotypes of 48 children with recurrent bacterial respiratory tract infections were determined. Fc gamma RIIa-H/H131 was less than half that observed in 123 healthy adults (P = .01). IgG2 responses were low in 25 of 48 patients after immunization with pneumococcal vaccine. These results suggest that Fc gamma RIIa polymorphism may contribute to increased susceptibility to infections with encapsulated bacteria in a childhood population with low IgG2 anti-carbohydrate antibodies.

Adolescent↗
PubMed1993

Granulocyte-macrophage colony-stimulating factor induces sequential activation and deactivation of binding via a low-affinity IgG Fc receptor, hFc gamma RII, on human eosinophils.

Eosinophils are important in antibody-mediated immune defense against parasites based on interaction with Ig receptors (FcR). Of the three classes of IgG FcR in humans, hFc gamma RI, II, and III, solely hFc gamma RII (CD32) is expressed on freshly isolated eosinophils. Despite an expression level similar to that found on monocytes and polymorphonuclear granulocytes, binding activity of hFc gamma RII on eosinophils is constitutively low. Freshly isolated eosinophils had a negligible ability to form rosettes with IgG-sensitized erythrocytes (EA-IgG). Addition of granulocyte-macrophage colony-stimulating factor (GM-CSF) caused an approximately threefold increase in EA-IgG rosettes. This increase was maximal after 35 minutes, and declined upon further incubation at 37 degrees C. Analysis of hFc gamma RII expression levels showed no significant changes and neither was the expression of other hFc gamma R classes induced. Blocking studies with anti-Fc gamma receptor monoclonal antibody (MoAb) proved hFc gamma RII specificity of enhanced IgG complex binding. These phenomena were not restricted to GM-CSF action, because the addition of interleukin-3 or interleukin-5 similarly enhanced EA-IgG binding. The kinetics of activation of hFc gamma RII binding activity were paralleled by the binding of EA-C3bi to CR3 on eosinophils. In contrast to the stable expression of hFc gamma RII during activation with GM-CSF, CR3 expression increased slowly. Ligand binding via both types of opsonin receptors proved receptor specific. However, the kinetics of enhanced binding via hFc gamma RII and CR3 suggested the possibility of a common mechanism underlying the enhancement of ligand binding via hFc gamma RII and CR3. This hypothesis was supported by the fact that binding via hFc gamma RII proved sensitive to both high concentrations of F(ab')2 fragments of anti-CD11b MoAb MO1 and chelation of bivalent cations with EDTA. In conclusion, our studies indicate that cytokines can induce a transient enhancement of hFc gamma RII binding activity. Qualitative, and not quantitative, changes in this receptor appear to underly the modulation of binding activity, which may be linked to changes in CR3 activity.

Cells, Cultured↗
PubMed1993

The human low affinity immunoglobulin G Fc receptor IIC gene is a result of an unequal crossover event.

We have isolated and characterized three genes coding for hFc gamma RIIA, IIB, and IIC. Each gene spans approximately 15-19 kilobases of DNA and consists of eight exons. Two exons encode the 5'-untranslated region and signal peptides, two exons code for homologous Ig-like extracellular domains, a single exon encodes the transmembrane spanning region, and three exons encode the cytoplasmic domains and 3'-untranslated regions. Analysis of gene structures support the concept that the hFc gamma RIIA and hFc gamma RIIB genes originated via gene duplication and divergence processes. The hFc gamma RIIC gene, however, showed a remarkable homology at its 5' end with the hFc gamma RIIB gene, whereas its 3' region was highly homologous with the hFc gamma RIIA gene, suggesting that the hFc gamma RIIC gene results from an unequal crossover event between the hFc gamma RIIA and IIB genes. This hypothesis was supported by nucleotide sequence analyses of the putative break-point region. The proposed site of recombination was located approximately 300 nucleotides downstream from the sixth (C1) exon. These data provide a unique model for the evolutionary generation of a receptor family with multiple biological functions.

Blotting, Southern↗
PubMed1993

Human IgG Fc receptor heterogeneity: molecular aspects and clinical implications.

Receptors for the Fc domain of IgG (Fc gamma R) provide a critical link between specific humoral responses and the cellular branch of the immune system. When hFc gamma R interact with immunoglobulin, a variety of biological responses are triggered. These include phagocytosis, endocytosis, antibody-dependent cellular cytotoxicity (ADCC), release of inflammatory mediators, and enhancement of antigen presentation. In the last few years our understanding of the Fc gamma receptor structure has increased dramatically, due to the availability of monoclonal antibodies (mAb) and cDNA probes. Fc gamma R are members of the immunoglobulin superfamily and three main classes, hFc gamma RI, hFc gamma RII, and hFc gamma RIII are recognized in man generating at least 12 different isoforms. A further level of complexity is introduced by various genetic polymorphisms and, importantly, recent evidence points at the relevance of this Fc gamma R heterogeneity.

Antibody-Dependent Cell Cytotoxicity↗
PubMed1993

Immunoadjuvant activity of a liposomal IL-6 formulation.

The adjuvant effect of interleukin 6 (IL-6) entrapped in liposomes was evaluated using a 65 kDa heat shock protein as a model antigen. The secondary humoral immune response either to antigen alone, or incorporated into liposomes, and the effect of IL-6 entrapped in liposomes, on this response were studied in Balb/c mice. The adjuvanticity of these formulations was compared with that of potent adjuvants such as Ribi and dimethyldioctadecylammoniumbromide (DDA). The importance of IL-6 during adjuvant activity was supported by the observation that high serum IL-6 levels were induced in Balb/c mice by all members of a panel of adjuvants tested. Following incorporation into liposomes, IL-6 retained its full biological activity, as shown by its capacity to sustain growth of the IL-6-dependent B9 cell line. At antigen dosages where Ribi and DDA gave minimal or no secondary antibody titres, incorporation of antigen into liposomes resulted in measurable secondary antibody titres. Interestingly, this adjuvant activity was significantly enhanced when liposomes containing IL-6 were co-injected with the liposomal antigen formulation. These results illustrate the potential adjuvant properties of this formulation, which seem especially useful for vaccines containing weak or non-immunogenic antigens.

Adjuvants, Immunologic↗
PubMed1993

Interaction of a human Fc gamma RIIb1 (CD32) isoform with murine and human IgG subclasses.

A group of Fc receptor molecules, classified CD32, recognize the Fc moiety of IgG with low affinity. We report the isolation and identification of different hFc gamma RIIb cDNA clones, amongst which are cDNA clones encoding hFc gamma RIIb1 and hFc gamma RIIb2. Two hFc gamma RIIb1 encoding cDNA clones (pIP9 and pIP14) were isolated, which differed by three nucleotides, probably because of allelic variation. The nucleotide differences result in one amino acid change between the allelic hFc gamma RIIb1 variants. This substitution is located at amino acid position 11 of the cytoplasmic tail; a tyrosine in hFc gamma RIIb1 (clone pIP9) was replaced by an aspartic acid in clone pIP14 (encoding hFc gamma RIIb1*). A complication in studying ligand specificity of Fc receptors is the potential co-expression of different classes, subclasses, or polymorphic forms of FcR on the same cell. We therefore used murine fibroblasts transfected with cDNA clone pIP14, encoding a hFc gamma RIIb1* isoform, as our model system. These fibroblasts were found to interact with erythrocytes sensitized with mIgG2a and mIgG2b in rosetting assays performed at 4 and 37 degrees C. Interestingly, hFc gamma RIIb1* transfectants bound mIgG1 sensitized erythrocytes only weakly at 4 degrees C, whereas profound binding was observed at 37 degrees C. The ligand specificity for human (h) IgG isotypes was found to be hlgG3 > or = hlgG1 > hlgG4 > hlgG2, as determined at 4 degrees C with hlgG dimeric complexes. However, when assayed at 37 degrees C, the binding of hlgG2 dimers increased significantly. Next, we evaluated whether these transfectants were capable of supporting anti-CD3 induced T cell proliferation.(ABSTRACT TRUNCATED AT 250 WORDS)

Alleles↗
PubMed1993

Isotype-specific cross-linking of select human Fc gamma R isoforms triggers release of IL-6.

Anti-CD3 MoAbs are widely used in T cell activation studies, and are effective in immunosuppressive therapy. We used a panel of mouse (m) anti-CD3 switch variant MoAbs of five different isotypes to study IL-6 release from accessory cells. Incubation of human (h) mononuclear cells with anti-CD3 MoAbs resulted in increased IL-6 levels with MoAbs of mIgG1 and mIgG2a isotypes, with no effect of mIgG2b or mIgA. This suggested involvement of IgG Fc receptors (Fc gamma R) in triggering IL-6 production. To evaluate the role of different Fc gamma R molecules individually we used a panel of hFc gamma R-transfected mouse fibroblasts, and Jurkat T cells as a model. IL-6 secretion by CD32 transfectants expressing the hFc gamma RIIa high-responder (HR) allelic form was triggered by mIgG1 anti-CD3 MoAb, with no effect of four other isotypes. None of the anti-CD3 MoAbs induced IL-6 secretion by CD32 transfectants expressing either a variant of this receptor, containing only a single intracellular amino acid (CT-), the hFc gamma RIIa low-responder (LR) allelic form, or hFc gamma RIIb1. hFc gamma RI (CD64) transfectants exhibited IL-6 production after incubation with mIgG2a anti-CD3 MoAb, and to a lesser extent with mIgG2b, and mIgG1 MoAb. Indirect involvement of T cells in triggering IL-6 secretion could be excluded by experiments in which transfectants were cultured with immobilized anti-CD3 MoAb. These data indicate that cross-linking of either hFc gamma RI, or hFc gamma RIIaHR by appropriate anti-CD3 MoAbs triggers IL-6 production of accessory cells, and not T cells. This may also take place in vivo during immunosuppressive therapy with anti-CD3 MoAbs, and related antibody-mediated immune responses.

3T3 Cells↗
PubMed1992

Human low-affinity IgG receptor Fc gamma RIIa (CD32) introduced into mouse fibroblasts mediates phagocytosis of sensitized erythrocytes.

Multiple isoforms of human (h) Fc gamma RII are currently recognized. We set up experiments to evaluate the significance of different hFc gamma RII (CD32) isoforms in the uptake of IgG-coated particles. Therefore, a panel of stable hFc gamma RII-transfected fibroblasts was constructed to study phagocytosis. It was observed that over 40% of 3T6 fibroblasts transfected with hFc gamma RIIa cDNA phagocytose human erythrocytes (E) coated with mouse (m) IgG1 or mIgG2a (EA). This was in contrast to cells expressing a tail-minus variant of Fc gamma RII (hFc gamma RIItail-). Fibroblasts transfected with hFc gamma RIIb1 cDNA infrequently internalized EA. There was no difference in EA binding by these transfectants; all three clones formed more than 80% EA-rosettes. Uptake of particles was dependent on the degree of E sensitization, and was inhibitable by CD32 monoclonal antibody AT10. Preincubation of cells with cytochalasin D blocked internalization completely, with no effect on binding. This shows that phagocytosis underlies the observed E internalization. Immunofluorescence studies using an anticathepsin D antiserum showed the maturation of phagosomes, containing antibody-coated E, into lysosomes. In conclusion, our studies show, for the first time, that fibroblasts possess the basic machinery for ingestion of erythrocytes, and are capable of phagocytosis only when equipped with an appropriate receptor. hFc gamma RIIa and, to a lesser extent hFc gamma RIIb1, are suited for this task, which seems dictated by the cytoplasmic domain.

Antigens, CD↗