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CD36 peptides enhance or inhibit CD36-thrombospondin binding. A two-step process of ligand-receptor interaction.

CD36 (glycoprotein IV or IIIB) is an integral plasma membrane protein of wide cellular distribution and functions as a receptor site for thrombospondin (TSP), an adhesive protein important in cell-cell and cell-matrix interactions. OKM5, a monoclonal anti-CD36 antibody, has been reported to block CD36 cell adhesive functions suggesting that the OKM5 epitope on CD36 is functionally important. A panel of 10 synthetic CD36 peptides was made. One peptide, P139-155, specifically inhibited the immunoadsorption of CD36 by OKM5, and P139-155 was directly immunoadsorbed by OKM5, indicating that CD36 sequence 139-155 represents part of the OKM5 epitope. TSP bound to immobilized P139-155 in a dose-dependent and saturable manner. Surprisingly, P139-155 significantly augmented, instead of inhibited, binding of CD36 to TSP. This peptide did not induce platelet aggregation but augmented ADP- and collagen-induced aggregation in platelet-rich plasma. Another CD36 peptide, P93-110, which had no effect on OKM5 immunoadsorption, blocked binding of CD36 to immobilized TSP and partially inhibited collagen-induced platelet aggregation. P93-110 by itself did not bind to TSP; however, in the presence of P139-155, there was a marked enhancement of P93-110 binding to TSP, with a stoichiometry consistent with the trimeric nature of TSP. The data suggest that CD36-TSP interaction is a two-step process; the sequence 139-155 region of CD36 binds first to TSP, triggering a change in TSP to reveal a second site, which binds the 93-110 region of CD36 with high affinity. CD36 peptides can be used as stimulators or inhibitors in cellular adhesive events involving TSP-CD36 interaction. Conformational changes leading to the exposure or activation of high affinity binding sites may occur in both the receptor and the ligand upon cell-cell and cell-matrix adhesion.

Amino Acid Sequence

Sense and antisense cDNA transfection of CD36 (glycoprotein IV) in melanoma cells. Role of CD36 as a thrombospondin receptor.

Thrombospondin (TSP) is a multifunctional matrix and platelet glycoprotein that interacts with cell surfaces and may play a role in mediating cell adhesion, platelet aggregation, platelet-monocyte interactions, cell proliferation, angiogenesis, tumor metastasis, and protease generation. To clarify and confirm the function of CD36 (glycoprotein IV) as a TSP receptor, we now describe a transfected cell model using human melanoma cells genetically manipulated by sense or antisense cDNA transfection to express either high or near zero levels of CD36. Surface expression was confirmed by flow cytometry with monoclonal anti-CD36 IgG and quantified by measuring radiolabeled antibody binding. Bowes melanoma cells, which in their wild type did not express CD36 and did not bind radiolabeled TSP, when transfected with the sense construct bound TSP in a 1:1 stoichiometric ratio with CD36 expression. Conversely, C32 melanoma cells, which in their wild type expressed high levels of CD36 and bound radiolabeled TSP at a 1:1 stoichiometric ratio, did not express CD36 and did not bind TSP when transfected with an antisense construct. In addition, transfected Bowes cells and wild type C32 cells, unlike wild type Bowes cells, adhered to activated platelets in a TSP-dependent manner. These data, i.e. the gain of function with sense cDNA transfection and loss of function with antisense transfection, strongly support the TSP receptor function of CD36. The distribution of this protein in vascular cells and tissues and observations that it may participate in signal transduction events suggest that TSP-CD36 interactions may play a role in mediating some of the pathophysiological processes associated with TSP.

Antibodies, Monoclonal

Structural, functional, and antigenic differences between bovine heart endothelial CD36 and human platelet CD36.

Endothelial cell CD36 (glycoprotein IV) has been purified from bovine heart tissue by detergent partitioning and immunoaffinity chromatography. Bovine CD36 differs from human CD36 in its apparent mass (85 versus 88 kDa), primary structure, and immunological cross-reactivity. Of the 18 N-terminal residues identified, 17 conformed to the human CD36 sequence. Mouse monoclonal antibodies E-1 and 8A6 defined bovine- and human-specific epitopes, respectively. Because human CD36 has been identified as a receptor for erythrocytes infected with the malaria parasite Plasmodium falciparum, we examined the ability of bovine CD36 to bind infected erythrocytes. Bovine CD36, unlike human CD36, did not bind infected erythrocytes, suggesting that human CD36-specific structural features are responsible for recognition of the infected erythrocyte ligand.

Amino Acid Sequence

CD36-mediated signal transduction in human monocytes by anti-CD36 antibodies but not by anti-thrombospondin antibodies recognizing cell membrane-bound thrombospondin.

Mononuclear cells (MNC) treated with anti-CD36 Fab or F(ab')2 fragments and then stimulated with anti-rabbit (F(ab')2 displayed an oxidative burst, suggesting that the crosslinking of CD36 promotes signal transduction in the absence of an Fc receptor involvement. Moreover, intact anti-TSP mediates a weak oxidative burst in MNC, which was strongly enhanced upon pretreatment of monocytes (but not lymphocytes) with TSP. This response, however, was mediated by Fc receptors, not by an involvement of CD36. Other means of crosslinking cell-bound TSP and exposure of MNC to surface-bound TSP failed to promote an oxidative burst. Crosscompetition tests confirmed that the interaction site(s) of TSP with monocytes are distinct from the signal-promoting sites recognized by polyclonal and 3 monoclonal anti-CD36 antibodies.

ADP-ribosyl Cyclase

Human dermal microvascular endothelial but not human umbilical vein endothelial cells express CD36 in vivo and in vitro.

CD36 is an 88-kDa glycoprotein that has been identified on platelets, monocytes, and some endothelial cells. Experimental evidence suggests that CD36 mediates the binding of Plasmodium falciparum-infected RBC to a variety of cells, and therefore may play a role in the vascular complications associated with malaria. Additionally, CD36 may also bind the extracellular matrix proteins thrombospondin and collagen. Human umbilical vein endothelial cells have been used in in vitro models examining the binding of P. falciparum RBC to endothelial cells, but they do not consistently express cell surface CD36. Inasmuch as human dermal microvascular endothelial cells (HDMEC) differ in a variety of ways from large vessel endothelial cells, we have examined HDMEC for cell surface expression of CD36 in vivo and in vitro. Direct immunofluorescence of skin showed bright staining of HDMEC with antibody recognizing CD36 and flow cytometric analysis of cultured HDMEC revealed cell surface expression. In contrast, large vessel endothelial cells were not stained with antibody recognizing CD36 in vivo and cultured cells derived from umbilical vein failed to express cell surface CD36 in vitro. Western immunoblots of lysates of HDMEC but not human umbilical vein endothelial cells demonstrated an 88-kDa protein that comigrated with CD36 from platelets. Functional studies demonstrated that adherence of PRBC to HDMEC was inhibited up to 66% by mAb recognizing CD36. Furthermore, the expression of CD36 on HDMEC was increased in a dose- and time-dependent manner by IFN-gamma, and was decreased by protein kinase C agonists. These data demonstrate that HDMEC express functionally active CD36 and this expression can be positively and negatively regulated by soluble factors. This study demonstrates that HDMEC are useful in the study of CD36-mediated binding of PRBC to endothelial cells in vitro and provides further evidence of distinct phenotypic differences between HDMEC and large vessel endothelial cells.

Antigens, CD

Normal human erythrocytes express CD36, an adhesion molecule of monocytes, platelets, and endothelial cells.

We have recently shown that rosetting of Plasmodium falciparum (MC R+ line)-infected erythrocytes (parasitized red blood cells [PRBCs]) with uninfected erythrocytes (RBCs) is blocked by coating of the RBCs with anti-CD36 monoclonal antibodies (MoAbs; Handunnetti et al, Blood 80:2097, 1992). Adult RBCs have previously been considered negative for CD36. However, using fluorescence-activated cell sorter analysis with the anti-CD36 MoAbs 8A6, OKM5, and OKM8, which reverse rosetting, we consistently detect CD36 on the majority of normal adult RBCs. Absorption of the MoAb solutions with CD36-transfected Chinese hamster ovary (CHO-CD36) cells removed the reactivity against both CHO-CD36 cells and RBCs, whereas absorption with CHO cells had no effect. By comparison with staining for glycophorin A, LFA-3, and CR1, the level of expression of CD36 appeared to be low. Nevertheless, normal RBCs were capable of adhering to plastic coated with anti-CD36 MoAbs. RBCs from one African malaria patient were identified as deficient in CD36 and these RBCs did not rosette with the patient's own P falciparum PRBCs, even though these PRBCs were capable of rosetting with RBCs from a normal donor in a CD36-dependent manner. Therefore, the level of expression of CD36 on normal RBCs is sufficient to be important in cell adherence, and may have a biologic role in normal individuals as well as in the pathology of P falciparum malaria.

Animals

Molecular basis of sequestration in severe and uncomplicated Plasmodium falciparum malaria: differential adhesion of infected erythrocytes to CD36 and ICAM-1.

The CD36 and ICAM-1 glycoproteins on vascular endothelial cells have been implicated as cytoadherence receptors for Plasmodium falciparum-infected erythrocytes (IRBC). Adhesion of IRBC from Thai patients with uncomplicated and severe falciparum malaria to purified CD36 or ICAM-1 and to C32 melanoma cells was compared. All malaria isolates bound to solid phase-adsorbed CD36 and to fluid-phase 125I-labeled CD36. IRBC adhesion to purified ICAM-1 varied widely, and no correlation with clinical severity of disease was observed. The cytoadherent phenotype of IRBC was modulated by selective panning on plates coated with purified CD36 or ICAM-1. IRBC selected by panning on CD36+, ICAM-1+ melanoma cells bound to cells that express surface CD36 but not to CD36-deficient cells, indicating that CD36 exerts a strong selective pressure on the IRBC cytoadherent phenotype. IRBC adhesion to CD36 and ICAM-1 suggests that P. falciparum parasites may use these receptors in vivo to promote parasite survival and immune evasion.

Animals

Molecular characterization of CD36 deficiency in blood donors of Middle Eastern and African origin reveals transcript-level defects beyond genomic variants.

BACKGROUND: The increasing diversity of blood donor populations has created new challenges for transfusion services worldwide. The identification of donors lacking relevant high-prevalence antigens is becoming increasingly important to ensure compatible blood products for alloimmunized patients and to support the development of rare donor registries. CD36 (ISBT 045) is a glycoprotein expressed on platelets, monocytes, and erythroid precursor cells. CD36 deficiency has been reported across multiple populations and is of relevance due to its association with anti-CD36 isoantibodies, which may cause platelet transfusion refractoriness and fetal/neonatal alloimmune thrombocytopenia. STUDY DESIGN AND METHODS: We analyzed CD36 expression in 1250 blood donors of diverse ancestry using flow cytometry. CD36-negative samples underwent molecular characterization using Sanger sequencing and next-generation sequencing of genomic DNA, complemented by cDNA analysis and cloning to investigate transcript-level alterations. RESULTS: We identified CD36 deficiency in 27 donors (2.16%). Genomic sequencing revealed 18 distinct coding variants, including three novel variants, most in the heterozygous state. In one CD36-negative donor, cDNA analysis demonstrated a 52-bp deletion in exon four and complete skipping of exon 9, despite the absence of splice-site variants in genomic DNA. Cloning confirmed coexistence of aberrant and wild-type transcripts in this individual. CONCLUSION: Our findings demonstrate that CD36 deficiency can arise from transcript-level defects in the absence of detectable coding or splice-site variants. These results indicate that genomic sequencing alone may be insufficient to fully resolve CD36-negative phenotypes and highlight the importance of integrating transcriptomic approaches to improve molecular diagnostics and transfusion support in increasingly diverse donor populations.

CD36 deficiency

A Common CD36 Variant and the Genetic Landscape of Dilated Cardiomyopathy in Individuals of African Ancestry.

IMPORTANCE: Dilated cardiomyopathy (DCM) is a major cause of heart failure that disproportionately affects individuals of African genetic ancestry (AFR), among whom familial clustering of disease is also more pronounced relative to those of European ancestry (EUR). However, established monogenic DCM genes, identified primarily in EUR populations, explain a smaller proportion of DCM cases in AFR populations. A recent study identified a common AFR-specific nonsense variant in CD36 that accounts for a substantial burden of DCM in AFR. How the risk and population impact of this variant compare with those of established genetic causes of DCM is unknown. OBJECTIVE: To compare the contribution of a CD36 nonsense variant to DCM risk with that of truncating variants in TTN and pathogenic or likely pathogenic (P/LP) variants in other established DCM genes. DESIGN SETTING AND PARTICIPANTS: Multicohort genetic association study including AFR and EUR participants with exome or genome sequence and DCM case status from four datasets: All of Us, Million Veteran Program, Penn Medicine Biobank, and the DCM Precision Medicine Study. EXPOSURE: Carrier status for TTN truncating variants, P/LP variants in 11 high confidence DCM genes, and the CD36 nonsense variant (Y325*; 0, 1, or 2 copies). MAIN OUTCOMES AND MEASURES: Odds of DCM; prevalence of risk-variant carriers among DCM cases; and population attributable fraction (PAF) for DCM. RESULTS: Among 82,623 AFR individuals across four studies, the mean age was 53.4 years and 1,625 had DCM. CD36 Y325* risk-allele homozygotes had 4.8-fold (95% CI, 3.1-7.3) increased odds of DCM, and CD36 Y325* heterozygotes had 1.4-fold (95% CI, 1.2-1.7) increased odds. TTN truncating variants also conferred elevated risk of DCM in AFR participants (OR, 8.46; 95% CI, 5.3-12.3). Among AFR DCM cases, 2.5% were CD36 homozygotes, second only to TTN truncating variants (4.3%) and exceeding all other high-confidence DCM genes combined (1.5%). In population-level analyses incorporating both heterozygous and homozygous CD36 Y325* carriers, the population-attributable fraction for CD36 (9.0%) surpassed that of TTN truncating variants (3.6%). CONCLUSIONS AND RELEVANCE: An ancestry-specific CD36 variant contributes more to DCM burden in AFR ancestry than established DCM genes, including TTN truncating variants, typically considered the most common genetic cause of DCM. These findings reshape the known genetic architecture of DCM in individuals of African ancestry and highlight the importance of representation in genomic research.

Journal Article

Thrombospondin sequence motif (CSVTCG) is responsible for CD36 binding.

To clarify the role of CD36 as a TSP receptor and to investigate the mechanisms of the TSP-CD36 interaction, transfection studies were performed using CD36-cDNA in a CDM8 plasmid. Jurkat cells transfected with CD36 cDNA express an 88kD membrane surface protein and acquire the ability to bind thrombospondin. The TSP amino acid sequence, CSVTCG, mediates the interaction of thrombospondin with CD36. CD36 transfectants but not control transfectants bind radiolabeled tyrosinated peptide (YCSVTCG). The hexapeptide inhibits thrombospondin expression on activated human platelets and results in diminished platelet aggregation. CSVTCG-albumin conjugates support CD36-dependent adhesion of tumor cells. We conclude that the CSVTCG repeat sequence is a crucial determinant of CD36 thrombospondin binding.

Amino Acid Sequence

Keratinocyte expression of CD36 antigen in benign and malignant epidermal cell-derived tumours.

Keratinocytes express the macrophage/monocyte antigen CD36 in a variety of inflammatory cutaneous diseases characterised by a T lymphocyte rich infiltrate. Since cell-mediated immune mechanisms also play a role in host responses to skin tumours, we investigated the presence of CD36 antigen on keratinocytes in a range of epidermal cell-derived benign and malignant tumours characterised by a peritumoural, dermal lymphocytic infiltrate. Frozen tissue sections of lesional tissue from a range of epidermally derived tumours were labelled with antibodies to CD1a, CD11b, CD36, and HLA-DR antigens. Benign and malignant squamoproliferative tumour cells exhibited a spectrum of CD36 expression, whereas those of basal cell origin were consistently CD36-. Suprabasal expression of CD36 was present in the normal perilesional epidermis of all tumours studied including basal cell carcinoma. Keratinocyte CD11b expression was not observed. The widespread presence of keratinocyte CD36 positivity in squamoproliferative, but not basal epidermal, tumours suggests its expression may be linked to the degree of keratinocyte differentiation. The stimulus for expression is unknown, but the fact that suprabasal perilesional epidermis expressed CD36 strongly in the absence of infiltrate suggests it may represent a non-specific response by keratinocytes to various stimuli.

Adult

Sequestrin, a CD36 recognition protein on Plasmodium falciparum malaria-infected erythrocytes identified by anti-idiotype antibodies.

The CD36 molecule expressed by human endothelial cells is a receptor for the adhesion of erythrocytes infected with the human malaria parasite Plasmodium falciparum. A CD36-specific monoclonal antibody, OKM8, inhibits the adhesion of malaria-infected erythrocytes (IRBC) to purified CD36 and cells expressing CD36. Monospecific polyclonal anti-idiotype (anti-Id) antibodies, raised against monoclonal antibody OKM8, expressed determinants molecularly mimicking the CD36 binding domain for the adhesion of IRBC. Purified rabbit anti-Id antibodies reacted with the surface of IRBC by immunofluorescence, directly supported the adhesion of wild-type P. falciparum malaria isolates, and inhibited IRBC cytoadherence to melanoma cells. An approximately 270-kDa protein was immunoprecipitated by the anti-Id antibodies from surface-labeled and metabolically labeled IRBC and was competitively inhibited by soluble CD36. These results support the hypothesis that CD36 is a receptor and the approximately 270-kDa protein, sequestrin, is a complementary ligand involved in the adhesion of IRBC to host-cell endothelium. Sequestrin is a candidate malaria vaccine antigen, and anti-Id antibodies that recognize this molecule may be useful for passive immunotherapy of cerebral and severe P. falciparum malaria.

Animals

Activation of monocytes and platelets by monoclonal antibodies or malaria-infected erythrocytes binding to the CD36 surface receptor in vitro.

The CD36 leukocyte differentiation antigen, recognized by MAbs OKM5 and OKM8 and found on human monocytes and endothelial cells, has been implicated as a sequestration receptor for erythrocytes infected with the human malaria parasite Plasmodium falciparum (IRBC). CD36 is also expressed on platelets and appears to be identical to platelet glycoprotein IV. We investigated receptor activation of monocytes and platelets by anti-CD36 MAbs and by IRBC. Incubation of human monocytes with anti-CD36 MAbs or IRBC resulted in stimulation of the respiratory burst as measured by reduction of nitroblue tetrazolium and generation of chemiluminescence. Incubation of human platelets with anti-CD36 MAbs resulted in platelet activation as measured by aggregation or ATP secretion. Activation of monocytes and platelets required appropriate intracellular transmembrane signaling and was inhibited by calcium antagonists or by specific inhibitors of protein kinase C or guanine nucleotide binding proteins. Soluble CD36 inhibited binding of IRBC to both monocytes and platelets, suggesting that these interactions are mediated by the CD36 receptor. Using a cytochemical electron microscopic technique, the presence of reactive oxygen intermediates was identified at the interface between human monocytes and IRBC. These data provide support for the hypothesis that reactive oxygen intermediates produced by monocytes when IRBC ligands interact with cell surface receptors may play a role in the pathophysiology of falciparum malaria.

Animals

CD36 Influences Leukemia Progression in MLL-AF9-Driven AML by Modulating the Leukemia Immune Microenvironment.

CD36, a fatty-acid translocase, is increasingly implicated in acute myeloid leukemia biology and treatment resistance, yet its contribution to leukemogenesis is still unclear. Using the MLL-AF9 model, we transduced hematopoietic stem/progenitor cells (HSPCs) from Cd36-knockout (KO) or wild-type (WT) mice and assessed leukemic potential with in vitro assays, transplants, and transcriptomic, metabolomic, and immune profiling. Both Cd36KO- and Cd36WT-HSPCs underwent efficient MA9-driven transformation, with comparable colony formation and Hox/Meis1 pathway activation, indicating Cd36 is dispensable for leukemic initiation. However, Cd36 deletion markedly attenuated disease progression, reducing leukemic burden and extending survival in irradiated mice (median 22 vs. 15 days, P = 0.001). Effects were strikingly amplified in immunocompetent, non-irradiated recipients (median 63 vs. 22 days, P = 0.002), revealing immune-dependent suppression. Immune profiling showed enhanced CD4⁺ and CD8⁺ T cell infiltration, reduced CD4⁺CD25⁺ regulatory-like cells, and lower Tim-3 expression in Cd36KO-MA9 spleens, consistent with a less exhausted, more effective anti-leukemic T cell response. Despite enhanced T cell infiltration, TCR repertoires remained conserved, indicating functional reprogramming rather than clonal selection. Consistent with a suppressive leukemia immune microenvironment, RNA-seq gene set enrichment analysis identified upregulation of inflammatory (TNFα/NF-κB) and hypoxic pathways in Cd36WT-MA9 cells. Untargeted metabolomics revealed metabolic shifts in Cd36KO cells, involving a reduction in three key metabolites, UDP-GlcNAc, UDP-Galactose/UDP-Glucose, and O-Phospho-L-Serine, that likely support an immune evasion mechanism. These findings demonstrate that while Cd36 is not essential for MLL-AF9-mediated transformation, its cell-intrinsic expression in leukemic cells suppresses anti-leukemic immunity and accelerates progression. This positions CD36 as a promising target to enhance immune surveillance and limit AML aggressiveness.

Acute Myeloid Leukemia (AML)

Phenotype, ultrastructure, and function of CD1+DR+ epidermal cells that express CD36 (OKM5) in cutaneous T-cell lymphoma.

This study investigated the phenotype and function of different antigen-presenting cells (APC) present within the epidermis of patients with cutaneous T-cell lymphoma (CTCL). Involved epidermis of CTCL compared with uninvolved was found to contain increased numbers of CD1+DR+ APC. This population was heterogeneous and comprised both leucocytes of a novel CD1+DR+CD36 (OKM5)+ phenotype and CD1+DR+CD36- indeterminate/Langerhans cells. The CD1+DR+CD36+ leucocytes did not express TcR-1, CD5, CD15, or CD22, and only a minor population expressed CD11, demonstrating that they were neither T nor B cells, and did not belong to the major CD11+ (OKM1+) blood monocyte population. Electron microscopy of purified CD36+ lesional epidermal cells (EC) demonstrated that they lacked Birbeck granules found on CD1(+)-selected Langerhans cells, and most cells exhibited features of indeterminate cells or macrophages. The capacity of EC from involved epidermis to present alloantigens was found to be increased relative to uninvolved epidermis in all patients tested, and this capacity was critically dependent upon the presence of CD45+DR+ bone marrow-derived cells but not on the presence of CD45-DR+ keratinocytes. Positive selection using MoAb against CD1 and CD36 demonstrated that both cell populations exhibited the capacity to stimulate T cells. The results indicate that a novel antigen-presenting cell population with a unique phenotype is present within involved skin of patients with mycosis fungoides. These cells express CD36 in addition to CD1 and have an ultrastructural appearance consistent with a dendritic antigen-presenting cell derivation.

Antibodies, Monoclonal

Epitopic heterogeneity of the CD36 antigen expressed by normal and neoplastic endothelial cells. An immunohistochemical study with a novel monoclonal antibody 8C9.

Phenotypic and functional heterogeneity of endothelial cells (ECs) is being recognized with increasing frequency. Here we report a novel murine monoclonal antibody (MoAb), named 8C9, that detects a unique epitope on the leukocyte differentiation antigen CD36 (platelet glycoprotein IV or IIIb) expressed by both normal and neoplastic ECs. In immunohistochemical and flow-cytometric studies, 8C9-immunoreactivity was detected on capillary ECs, adipocytes, monocytes, platelets and a human monocytoid cell line U-937, which are known to express the CD36 antigen. Blocking experiments using U-937 cells and studies on cryostat sections revealed that a murine MoAb OKM5, which detects the CD36 antigen, blocked the binding of 8C9 to its antigen. Immunoblot analysis showed that 8C9 bound to a 97-kDa membrane protein expressed by U-937 cells treated with phorbol ester. These results indicate that 8C9 detects the CD36 antigen. However, the findings that some OKM5-positive normal ECs in the liver, spleen and lymph nodes as well as neoplastic ECs in a cutaneous angiosarcoma did not react with 8C9, together with the fact that the CD36 antigen does not form a complex or associate with other proteins, suggest epitopic heterogeneity of the CD36 antigen expressed by these tissues.

Antibodies, Monoclonal

Involvement of CD36 on erythrocytes as a rosetting receptor for Plasmodium falciparum-infected erythrocytes.

Plasmodium falciparum-infected erythrocytes (parasitized red blood cells [PRBCs]) can adhere to uninfected erythrocytes (RBCs) to form rosettes, and adhere to the endothelial cell (EC) surface antigen CD36. These adherence phenomena have previously been considered quite different. We show that anti-CD36 monoclonal antibodies (MoAbs) reverse rosetting of PRBCs from both a culture-adapted line (Malayan Camp [MC] strain) and a natural isolate, GAM425. Three MoAbs that block adherence of PRBCs to ECs or C32 melanoma cells also reversed rosetting by greater than 50% at levels of less than 1 microgram/mL (OKM5, OKM8, and 8A6). Two other MoAbs that react with purified CD36 (1D3 and 1B1), but do not react with the surface of C32 cells, failed to reverse rosetting. When rosettes were disrupted and the RBCs and PRBCs were pretreated separately with antibodies before mixing to allow rosette reformation, only pretreatment of RBCs had an effect. MoAb 8A6 pretreatment of RBCs blocked rosette reformation, while MoAb 1B1 pretreatment did not. Rosetting was also reversed by purified human platelet CD36. In conjunction with evidence that CD36 is expressed on normal human erythrocytes (van Schravendijk et al, Blood 80:2105, 1992), we conclude that this CD36 is able to act as a host receptor for rosetting in the MC strain and some natural isolates of P falciparum.

Animals

Keratinocyte and epidermal leukocyte expression of CD36 (OKM5) in benign and malignant skin diseases.

CD36 recognizes a 88 Kd glycoprotein, found on different cell populations involved in immunoregulation and are induced on keratinocytes by in vitro treatment with gamma-interferon. Therefore, we obtained skin biopsies from 48 patients with various dermatological diseases and from 5 healthy volunteers and stained these with monoclonal antibodies OKM5 (CD36), anti-HLA-DR and OKT6 (CD1a) using a three stage immunoperoxidase method. In normal skin, CD36 expression was not observed. In contrast, keratinocytes in diseased skin were CD36+. In most cases, the staining was restricted to the stratum granulosum and the stratum spinosum, but in psoriasis, squamous cell carcinoma and lymphomatoid papulosis, more extensive staining of keratinocytes was seen. In addition, CD36+ epidermal leukocytes were found in allergic patch-test infiltrates and in mycosis fungoides. The findings of CD36 expression by epidermal cells within a broad spectrum of dermatological diseases indicate a role for these cells in the regulation of immune reactions in the skin.

Antibodies, Monoclonal