A strong association between HLA-B*5101 and Behçet's disease in Greek patients

Behçet's disease is known to be associated with HLA-B51, one of the split antigens of HLA-B5, among many different ethnic groups. In a Greek population, an increased incidence of HLA-B5 in the patient group has also been reported. Because the B51 antigen has been recently identified to comprise seven alleles, B*5101-B*5107, we performed HLA-B51 allele genotyping by the PCR-SSP method as well as serological HLA-A and -B typing among 31 Greek patients with Behçet's disease to investigate whether there is any correlation between one particular B51-associated allele and Behçet's disease. The frequency of B51 was remarkably high (80.6%) in the patient group as compared to the ethnically matched control group (26.7%). In addition, HLA-A26 was also increased in the patients (29.0%) as compared with the healthy controls (3.3%). B51 allele genotyping revealed that all these B51-positive patients carried B*5101. This study revealed a strong association of Behçet's disease in Greeks with one of the B51 subantigens, providing insight into the molecular mechanism underlying an HLA association with Behçet's disease.

Precise switching of DNA replication timing in the GC content transition area in the human major histocompatibility complex

The human genome is composed of long-range G+C% (GC%) mosaic structures thought to be related to chromosome bands. We previously reported a boundary of megabase-sized GC% mosaic domains at the junction area between major histocompatibility complex (MHC) classes II and III, proposing it as a possible chromosome band boundary. DNA replication timing during the S phase is known to be correlated cytogenetically with chromosome band zones, and thus the band boundaries have been predicted to contain a switch point for DNA replication timing. In this study, to identify to the nucleotide sequence level the replication switch point during the S phase, we determined the precise DNA replication timing for MHC classes II and III, focusing on the junction area. To do this, we used PCR-based quantitation of nascent DNA obtained from synchronized human myeloid leukemia HL60 cells. The replication timing changed precisely in the boundary region with a 2-h difference between the two sides, supporting the prediction that this region may be a chromosome band boundary. We supposed that replication fork movement terminates (pauses) or significantly slows in the switch region, which contains dense Alu clusters; polypurine/polypyrimidine tracts; di-, tri-, or tetranucleotide repeats; and medium-reiteration-frequency sequences. Because the nascent DNA in the switch region was recovered at low efficiency, we investigated whether this region is associated with the nuclear scaffold and found three scaffold-associated regions in and around the switch region.

Triplet repeat polymorphism in the NOTCH4 gene with the human major histocompatibility complex in a healthy population and patients with a salivary gland tumor in Japan

The NOTCH4 gene, the human counterpart of the mouse mammary tumor gene, int-3, has been recently localized near the boundary of the HLA class II and class III regions. This gene is one of candidates for development of salivary gland tumor. Microsatellite polymorphism of (CTG)n repeat in the signal peptide domain of NOTCH4 was analyzed in Japanese including the patients with salivary gland tumor. Four alleles consisting of 6, 9, 10 and 11 repetitions of CTG (Leu) were observed and found to be in linkage disequilibria with HLA class I and class II alleles. No significant association of this microsatellite polymorphism with the disease were observed in 26 samples of salivary gland tumor. In this neoplasia, neither large-scale deletion nor translocation was detected around the NOTCH4 gene using genomic Southern hybridization analysis by the NOTCH4 cDNA as a probe.

Physical mapping 220 kb centromeric of the human MHC and DNA sequence analysis of the 43-kb segment including the RING1, HKE6, and HKE4 genes

A cosmid contig was constructed from a YAC clone with a 220-kb insert that spans the centromeric side of the human MHC class II region, corresponding to the mouse t complex. The gene order was identified to be HSET-HKE1.5-HKE2-HKE3-RING1-HKE6- HKE4 (RING5). The genomic sequence of a 42,801-bp long region encoded by one cosmid clone in the RING1, HKE6, and HKE4 subregions was determined by the shotgun method. The exon-intron organization of these three genes, RING1 (Ring finger protein), HKE6 (steroid dehydrogenase-like protein), and HKE4 (transmembrane protein with histidine-rich charge clusters), was determined. The previously reported RING2 gene was revealed to be identical to HKE6. Transcripts from HKE4 were detected in the placenta, lung, kidney, and pancreas. Those of HKE6 were found in the liver and pancreas. The 25-kb region proximal to the RING1 gene includes an extensive dense cluster of Alu repeats (about 1.2 Alu per kb), and no gene has been identified in this so far. The region is equivalent to part of the mouse t complex and could be of relevance to human development.

Nucleotide sequence analysis of the HLA class I region spanning the 237-kb segment around the HLA-B and -C genes

To elucidate the detailed gene organization of the human leukocyte antigen (HLA) class I region on chromosome 6, seven contiguous cosmid genomic clones covering the 237-kb segment around the HLA-B and -C loci were subjected to DNA sequencing by the shotgun strategy to give a single contig of 236,822 bp from the MICA gene (58.2 kb centromeric of HLA-B) to 90.8 kb telomeric of HLA-C. This region was confirmed to contain four known genes, MICA, HLA-17, HLA-B, and HLA-C, from centromere to telomere. Further, a new member of the P5 multicopy genes was found to be about 1.3 kb upstream of the HLA-17 gene and designated P5.8. Five novel genes designated NOB1-5 were identified by RT-PCR and Northern blot hybridization. In addition, two pseudogenes, dihydrofolate reductase pseudogene (DHFRP) and ribosomal protein L3 homologous gene (RPL3-Hom), were also found in the vicinity of the HLA-B and -C genes, respectively. The two segments (about 40 kb) downstream of the HLA-B and HLA-C genes showed high sequence homology to each other, suggesting that segmental genome duplication including the major histocompatibility complex (MHC) class I gene must have occurred during the evolution of the MHC.

MICA gene and ankylosing spondylitis: linkage analysis via a transmembrane-encoded triplet repeat polymorphism

In order to address the possibility that the MICA gene located 47 kb upstream from HLA-B is involved in the pathogenesis of ankylosing spondylitis (AS), we have investigated microsatellite polymorphism in the transmembrane region of MICA in Caucasian patients with AS. The microsatellite allele consisting of 4 repetitions of GCT/AGC was present at significantly higher frequency in the patient group (Pc<0.0000001) than in the ethnically matched control group. However, the frequency of the (GCT/AGC)4 allele was significantly low in the B27-positive patients than in the B27-positive healthy controls (Pc=0.0145). These observations suggest that B27 itself remains the primary genetic marker for AS, although the significantly dissimilar phenotype frequency of the (GCT/AGC)4 allele in B27-positive patients and healthy individuals may reflect the existence of other genetic factor(s) in the HLA-B27 haplotype involved in the development of AS.

Molecular genetic analysis of HLA class II alleles in Japanese patients with melanoma

Distribution of HLA-DQA, -DQB and -DPB alleles in ninety-six Japanese patients with melanoma was analyzed using the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method, and the association between clinical parameters and the presence of certain HLA class II alleles investigated. The frequency of HLA-DQB1*0302 was increased, while those of DQA1*0101(04), -DQA1*0401 and DRB1*0802 were decreased in melanoma patients compared with controls. Moreover, the frequency of HLA-DQA1*0103 in patients with acral lentiginous melanoma was increased compared with controls. However, none of these HLA class II alleles showed significant positive or negative associations after correction of the P value. In addition, there was no correlation between these antigens and clinical parameters. These results indicate that HLA class II alleles may not contribute to a strong susceptibility to melanoma in the Japanese.

Identification of a novel HLA-B allele (B*4202) in a Saudi Arabian family with Behçet's disease

A new HLA-B antigen, tentatively called HLA-B42AND, was identified as a B42 serologic variant in a Saudi Arabian family. DNA sequencing analysis of the second and third exon of this new B allele revealed that B42AND was identical to B*4201 except for a single T to C substitution at position 97 of exon 2. This substitution results in histidine (CAC) at codon 9 in B42AND instead of tyrosine (TAC) in B*4201. The antigen frequency of B42AND in a Saudi Arabian population was around 10%. This novel B42AND has officially been named HLA-B*4202.

Trinucleotide repeat polymorphism within exon 5 of the MICA gene (MHC class I chain-related gene A): allele frequency data in the nine population groups Japanese, Northern Han, Hui, Uygur, Kazakhstan, Iranian, Saudi Arabian, Greek and Italian

We recently identified a trinucleotide repeat polymorphism, (GCT)n, within the transmembrane (TM) segment of the human MHC class I MICA gene (MHC class I chain-related gene A). Five distinct alleles (A4, A5, A5.1, A6, A9) corresponding to 4, 5, 5 with one nucleotide insertion, 6 and 9 repetitions, respectively, have been detected in various HLA-homozygous B cell lines. Here we present allele frequencies for this trimeric short tandem repeat (STR) in 604 unrelated individuals collected from nine human populations (Japanese, Northern Han, Hui, Uygur, Kazakhstan, Iranian, Saudi Arabian, Greek and Italian) determined using the polymerase chain reaction (PCR) combined with fluorescent-based automated fragment detection technology. All alleles were present in each population, but allelic distributions varied from one population to another. No new alleles (such as A7 or A8) were identified. The evolutionary and structural significance of these data as well as the potential application to forensic medicine is discussed.

Gene organization of human NOTCH4 and (CTG)n polymorphism in this human counterpart gene of mouse proto-oncogene Int3

The cDNA and genomic clones for the human counterpart of the mouse mammary tumor gene Int3 were isolated and sequenced. We designated this human major histocompatibility complex (MHC) class III gene as NOTCH4, since very recently, by sequencing cDNA clones, the complete form of the mouse proto-oncogene Int3 has been clarified and named Notch4. The present human NOTCH4 sequence is the first example of the genomic sequence for the extracellular portion of the mammalian Notch4, and by comparing it with the mouse Notch4 cDNA sequence, the exon/intron organization was clarified. The comparison of the predicted amino acid sequence of human NOTCH4 with those of other Notch homologues of a wide range of species revealed four subfamilies for mammalian Notch. In the protein coding region of human NOTCH4, we found (CTG)n repeats showing a variable number tandem repeat (VNTR) polymorphism for different human leukocyte antigen (HLA) haplotypes. Ten genes mapped on 6p21.3, including NOTCH4, were found to have counterparts structurally and functionally similar to those mostly mapped on 9q33-q34, indicating segmental chromosome duplication during the course of evolution. Similarity of genes on chromosomes 1, 6, 9 and 19 was also discussed.

Triplet repeat polymorphism in the transmembrane region of the MICA gene: a strong association of six GCT repetitions with Behçet disease

A member of a novel family of the human major histocompatibility complex (MHC) class I genes termed MIC (MHC class I chain-related genes), MICA, has been recently identified near the HLA-B gene on the short arm of human chromosome 6. The predicted amino acid sequence of the MICA chain suggests that it folds similarly to typical class I chains and may have the capacity to bind peptides or other short ligands. Therefore, MICA is predicted to have a specialized function in antigen presentation or T cell recognition. During nucleotide sequence analyses of the MICA genomic clone, we found a triplet repeat microsatellite polymorphism of (GCT/AGC)n in the transmembrane (TM) region of the MICA gene. In 68 HLA homozygous B cell lines, 5 distinct alleles of this microsatellite sequence were detected. One of them contained an additional one base insertion that created a frameshift mutation resulting in a premature termination codon in the TM region. This particular allele may encode a soluble, secreted form of the MICA molecule. In addition, we have investigated this microsatellite polymorphism in 77 Japanese patients with Behcet disease, which is known to be associated with HLA-B51. The microsatellite allele consisting of 6 repetitions of GCT/AGC was present at significantly higher frequency in the patient group (Pc = 0.00055) than in a control population. Furthermore, the (GCT/AGC)6 allele was present in all B51 positive patients and in an additional 13 B51 negative patients. These results suggest the possibility of a primary association of Behcet disease with MICA rather than HLA-B.

HLA-DRB4 genotyping by PCR-RFLP: diversity in the associations between HLA-DRB4 and DRB1 alleles

The serologically defined HLA-DR53 antigen is associated with HLA-DR4, -DR7, and -DR9 antigens, and these haplotypes contain two functional genes, DRB1 and DRB4, and two pseudogenes, DRB7 and DRB8. The DRB4 gene encodes the DR53 antigen, and has been officially recognized to contain three allelic variants (DRB4*0101, 0102, and 0103). In this study, we have established the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method for DRB4 genotyping and analyzed genetic polymorphism of the DRB4 gene in Japanese population. DRB4*0101, DRB4*0102, and DRB4*0103 could be observed at the frequencies of 0.5%, 1.1% and 32.7%, respectively. The same DRB1 allele does not necessarily share an identical DRB4 allele. Further, a tight linkage disequilibrium was found between DRB4*0102 and DRB1*0401 in Japanese population, whereas DRB1*0401 was associated with DRB4*0101 or *0103 in Caucasian population. These findings reveal extensive diversity of the HLA-DRB1 and -DRB4 haplotypes and may have important implications for HLA-disease associations and donor selection in unrelated transplantation.

Analysis of allelic variation of the TAP2 gene in sarcoidosis

Sarcoidosis is a systemic granulomatous disease and the DRB1 gene of the DR subregion has been implicated for determining the genetic susceptibility to the disease. We evaluated the allelic variation of the TAP2 gene using the PCR-RFLP method as well as the mismatched PCR-RFLP method in 82 Japanese patients with sarcoidosis and 92 healthy controls. A new allele, TAP2*0103 and a new polymorphic variation at codon 577 in addition to TAP2*0101, TAP2*0102 and TAP2*0201 have been recognized in the Japanese subjects. No significant differences were observed in the frequencies of any TAP2 alleles or dimorphism at codon 577 between the patients and healthy controls. Polymorphic variation of the TAP2 gene does not confer the susceptibility to sarcoidosis.

Immunogenetic study of sympathetic ophthalmia

Sympathetic ophthalmia (SO) is very rare but it remains one of the most intractable eye diseases. In clinical manifestations and histopathologic features SO is known to resemble closely Vogt-Koyanagi-Harada's disease (VKH disease). We had reported that VKH disease was significantly associated with HLA-DRB1*04 and -DQB1*04 in Japanese patients. In this study, to investigate an HLA association with SO we performed HLA serological and PCR-based DNA typing in 16 patients and 50 healthy controls. Our study revealed that HLA-DRB1*04 (0405; Pc < 5 x 10(-4)), DQA1*03 (Pc < 5 x 10(-3)), and DQB1*04 (0401; Pc < 5 x 10(-4)) were significantly associated with SO as compared to the healthy controls but there was no significant difference in the frequencies of any DPB1 alleles between the patients and healthy controls. It can be postulated that not only the clinical manifestations but also the genetic predisposition of SO are very similar to those of VKH disease.

Haplotypic diversity of DQA1*03 and *05 subtypes differing at amino acid residue 160 encoded in the third exon in 2215 Japanese individuals

We analyzed the frequencies and haplotypes of DQA1*03 and *05 subtypes, DQA1*03011 or DQA1*0302 and DQA1*0501 or DQA1*0503, respectively, differing only at codon 160 in the non-polymorphic third exon of the DQA1 gene. Of these, 1,862 and 337 individuals selected as DQA1*03- and DQA1*05-positive samples, respectively among 2,215 unrelated Japanese were typed for their nucleotide variation at residue 160 using PCR-SSP. As observed in other populations, all the samples carrying DQA1*03011 (Gene Frequency, GF: 7.8%) were found to share DQB1*0302, whereas those carrying DQA1*0302 (GF: 44.3%) were associated with a variety of DQB1 alleles including DQB1*0302. Both of the DQA1-DQB1 haplotypes with DQA1*03011 and DQA1*0302 carrying DRB1*0406, DQA1*03011-DQB1*0302 and DQA1*0302-DQB1*0302, showed a strong linkage disequilibrium with B62 (p < 0.001, p < 0.05). These results suggested that DQA1*03011 was generated from a single amino acid change at residue 160 in the DQA1*0302-DQB1*0302 haplotype. However, none of the haplotypes with two different DQA1*03 subtypes carrying DRB1*0403,*0405,*0802 and *0901 showed a linkage disequilibrium with any common B-locus antigens, revealing extensive haplotypic diversity of the DQA1*03 group. For example, DRB1*0802 haplotypes showed linkage disequilibria with two different B-locus antigens, B35 and B61 depending on the presence of DQA1*03011 and DQA1*0302, respectively. The GFs of DQA1*0501 and *0503 were 5.1% and 2.7%, respectively. The DQA1*05 associated haplotypes in the DR52-antigen group with DQB1*0301 were divided into two groups, depending on the bimorphism at residue 160. Such a high degree of haplotypic diversity in association with DRB1 and B alleles observed in the DQA1*03 and *05 groups related to amino acid variation at residue 160, which may affect biological function such as the interaction between CD4 and HLA-DQ molecules, seems to reflect selective pressure in the evolutionary process of HLA antigens.

Pathogenic gene responsible for the predisposition of Behçet's disease

HLA-B51 is well known to be associated with Behçet's disease (BD) in many different ethnic groups. The hypothesis may be presented that B51 molecules are primarily involved in BD development through specific antigen presentation. Furthermore, HLA-C genotyping by the polymerase chain reaction-sequence specific primers method suggests that the BD pathogenic gene is not the HLA-C gene itself but some other gene located near the HLA-B gene. Polymorphic analysis of the Tau-a microsatellite between the HLA-B and TNF genes indicates that the pathogenic gene of BD is not the HLA-B51 gene itself but other gene located around the HLA-B gene. Recent studies suggest that many novel genes exist in the region between the TNF and HLA-B or HLA-C genes such as MIC and PERB, etc. and furthermore, many unidentified new genes have been suggested to exist in this region. In this paper, the present situation of the investigations on the genetic predisposition responsible for BD was reviewed.

LMP7 polymorphism in Japanese patients with sarcoidosis and Behçet's disease

To evaluate the influence of the MHC-linked LMP7 gene on disease susceptibility in HLA class I and class II-associated diseases, the distribution of LMP7 alleles was determined using the PCR-RFLP method in 69 Japanese patients with Behçet's disease, 65 patients with sarcoidosis, and 100 unrelated healthy controls. No differences were found between either of the patient groups and the healthy control group, indicating that LMP7 allelic variation may not contribute to the pathogenesis of either Behçet's disease or sarcoidosis. We also analyzed linkage disequilibria between LMP7 and HLA class II alleles in Japanese populations.

Cloning, sequencing, and chromosomal localization of two tandemly arranged human pseudogenes for the proliferating cell nuclear antigen (PCNA)

We have characterized a human genomic clone carrying two pseudogenes for the proliferating cell nuclear antigen (PCNA), which were tandemly arranged on human Chromosome (Chr) 4. One is a processed pseudogene that showed a 73% nucleotide homology to the human PCNA cDNA and possessed none of the introns existing in the functional PCNA gene. This pseudogene presumably arose by reverse transcription of a PCNA mRNA followed by integration of the cDNA into the genome. The other is a 5' and 3' truncated pseudogene that showed a nucleotide homology to a 3' region of the exon 4 and to a 5' region of the exon 5 of the PCNA gene and did not have the intronic sequence between the exons 4 and 5. Both pseudogenes had the same nucleotide deletion as compared with the human functional PCNA gene. A phylogenetic analysis of PCNA gene family, including the functional PCNA gene and another PCNA pseudogene located on a different chromosome, revealed that the truncated pseudogene exhibits the closest evolutionary relationship with the processed pseudogene, suggesting that the truncated pseudogene was generated by duplication of the processed pseudogene after translocation to Chr 4. Furthermore, fluorescence in situ hybridization revealed that these pseudogenes are located on the long arm of Chr 4, 4q24.

HLA class I antigens in Japanese patients with melanoma

In this study, we analyzed the frequencies of human leukocyte antigen (HLA) class I alleles in 110 Japanese patients with melanoma using serological methods, and compared such frequencies with clinical parameters. As expected, frequencies of HLA allele distribution in patients with melanoma reflected the frequencies observed in the normal Japanese population. Because these are different from populations belonging to other races (e.g., white), it followed that the HLA allele distribution in melanoma patients varies among different races. This differences may have significant implications for T-cell-mediated, HLA-restricted therapeutic modalities. No significant associations between HLA and clinical parameters were noted in this study. This report may help design future clinical trials involving therapeutic approaches based on HLA-restricted mechanisms.

Seroepidemiological studies on Silk Road ethnic groups

To clarify the origin of the Japanese, the Jomom and/or Yayol, we screened for HTLV-1 and -II antibodies among inhabitants of the Silk Road, the Han, Uygur and Kazaks. We also screened for HIV, HBV, and HCV. The HTLV-I, -II, HIV, and HCV antibody tests were uniformly negative in all the studied groups. In contrast, a significantly higher incidence of HBs antigen was observed in all the groups tested (Northern Han: 11.9%, Uygur: 6.0%, Kazak: 9.1%). These results indicate that these ethnic groups are not the origin of the indigenous Japanese (the Jomon), and that HBV is prevalent in the various groups along the Silk Road.

HLA-C genotyping of patient with Behçet's disease in the Japanese population

Behçet's disease has been known to be strongly associated with a particular HLA-B allele, B51. To address the possibility that the HLA-C gene, which is closely linked to HLA-B but has been poorly defined for allo-antigen specificity by the serologic method is involved in the susceptibility to Behçet's disease, HLA-C genotyping was performed for 90 Japanese Behçet's disease patients by the PCR-SSP method. The frequencies of HLA-Cw*14 and -Cw*15 were significantly higher in the patient with Behçet's disease as compared to the controls (48.9% vs. 24.0%, p = 0.0005, and 17.8% vs. 7.3%, p = 0.0434, respectively). On the other hand, the frequencies of HLA-Cw*0304 and -Cw*01 were significantly decreased in the patient group as compared to the control group (7.8% vs. 25.0%, p = 0.0027, and 23.3% vs. 37.5%, p = 0.0398, respectively). The significantly higher HLA-Cw*14 and -Cw*15 alleles may tightly correlate with the B51 antigen, and hence may have increased as a result of a linkage disequilibrium with B51. Accordingly, the HLA-C allele frequencies were compared for the B51-positive or -negative patients and controls, but there was no HLA-C allele showing a significant difference between these patient and control groups. Conversely, analysis of the HLA-B allelic distribution in association with HLA-Cw*14 revealed that in the healthy controls, B44 and B51 were present at the frequencies of 57.1% and 35.7% of the HLC-Cw*14-positive individuals, respectively. In contrast, in the Cw*14-positive patients the frequency of B44 was merely 14.0% (p = 0.0001) and that of B51 was significantly high, amounting to 82.0% (p = 0.0001). These facts suggest that the pathogenic gene of Behçet's disease is not the HLA-C gene (HLA-Cw*14 and/or HLA-Cw*15) but the HLA-B gene (HLA-B51) itself or a non-HLA gene residing in the centromeric side of the HLA-B gene rather than in the telomeric side around the HLA-C gene. This finding supports our previous mapping result, which located the susceptible gene between the TNF and HLA-B genes.

Human leukocyte antigen-DRB1*1502 (DR2Dw12) transgene reduces incidence and severity of arthritis in mice

A strong correlation exists between susceptibility to RA in humans and some DRB1 alleles of the MHC region, such as DRB1*0401 and DRB1*0101. Meanwhile, incidences of other DR specificities, such as DR2, DR5, or DR7 have often been found reduced among RA patients. Like RA, susceptibility to mouse CIA is influenced by the MHC class II loci. To analyze the effect of a DRB1 molecule associated with low incidence of RA on mouse CIA, a human DRB1*1502 (DR2Dw12) transgene was introduced into CIA-susceptible B10.RQB3 (H2Aq) mice. Transgene-positive DRB1*1502 mice showed a significant reduction in the incidence and severity of arthritis. Moreover, the clinical reduction of arthritis correlated with the T-cell proliferative response of B10.RQB3-DRB1*1502 mice against a self-derived DRB1 peptide from the third hypervariable region. Our results suggest that the DRB1*1502-mediated protection against CIA can be explained by the DRB1 molecule acting as a source of self-antigenic peptide which interferes with the T-cell response against immunodominant regions(s) of the arthritogenic type II collagen molecule. By analogy, a similar mechanism might play a critical role in influencing the class II-associated predisposition to RA.

A novel monoclonal antibody mNI-58A against the alpha-chain of leukocyte function-associated antigen-1 (LFA-1) blocks the homotypic cell aggregation and actively regulates morphological changes in the phorbol myristate acetate (PMA)-activated human monocyte-like cell line, U937

A monoclonal antibody (mAb), designated mNI-58A, was produced by immunizing mice with the lipopolysaccharide (LPS)-stimulated monocyte-like cell line, U937. The antigen defined by mNI-58A was widely expressed on various lymphoid cells and all cell lines examined except the erythroid cell line, K562. When the reactive patterns between mNI-58A and the mAbs to various human differentiation antigens (CD11a, CD11b, CD11c, CD14, CD16, CD18, CD23, CD28, CD29, CD31, CD43, CD44, CD45RA, CD50, CD54, CD58, CD80, CD102, CD106, HLA-class I and-class II antigen) were compared, that of mNI-58A was found to be similar to those of the leukocyte function-associated antigen-1 (LFA-1) mAbs. Using a competitive immunofluorescence binding assay it was found that the preincubation with one of the CD11a mAbs, 2F12 completely blocked the subsequent binding of mNI-58A. mNI-58A prevented the homotypic cell aggregation of the phorbol myristate acetate (PMA)-activated U937 cells (referred to as PMA-U937) and PMA-activated Epstein-Barr virus (EBV)-transformed B cell lines, B-85 and Mann. mNI-58A markedly induced the spread formation of the PMA-U937 cells following this blocking of the homotypic cell aggregation, whereas 2F12 did not under the same condition. The spread formation induced by mNI-58A was completely blocked by cytochalasin B (CyB), cytochalasin D (CyD), cycloheximide (CHX) or protein kinase C inhibitors, sphingosine and H-7. The U937 cells markedly adhered to the tumor necrosis factor-alpha (TNF-alpha)-stimulated human umbilical vein endothelial cells (HUVECs) and also to the extracellular matrix protein, fibronectin, but mNI-58A did not enhance or block these adhesion process. mNI-58A precipitated two glycoproteins with molecular weight 180 kDa and 95 kDa as determined by SDS-PAGE analysis, which were identical to the LFA-alpha (CD11a) and beta (CD18) chains of leukocyte integrin precipitated by the CD11a mAbs, respectively. Sequential immunoprecipitation studies using the CD11a mAb (2F12) also indicate that mNI-58A recognizes an epitope on the alpha-chain of the LFA-1 molecule. The ability of mNI-58A to block the PMA-U937 cells and to induce the spread formation of these cells suggests that mNI-58A is a novel mAb reacting with an epitope on the alpha-chain of LFA-1 different from those recognized with the existing CD11a mAbs.