VS38: a new monoclonal antibody for detecting plasma cell differentiation in routine sections

The plasma cell associated antigen detectable by antibody VS38 is the p63 rough endoplasmic reticulum protein

AIMS

To characterise the 64 kDa intracellular antigen present on normal and neoplastic plasma cells detected by monoclonal antibody VS38 and by another antibody, MC186, of similar reactivity.

METHODS

The VS38 monoclonal antibody was used to screen a bacterially expressed peripheral blood cDNA library, and the immunocytochemical staining of the two antibodies was compared with those raised specifically to the protein identified as the VS38 antigen.

RESULTS

A partial cDNA encoding the VS38 antigen was cloned and shown to be identical to the human p63 gene. p63 is a non-glycated, reversibly palmitoylated type II transmembrane protein which is found in rough endoplasmic reticulum. Antibody MC186 also recognised this protein and both VS38 and MC186 together with two antibodies raised to p63 gave identical immunostaining patterns.

CONCLUSIONS

The VS38 antigen was identified as the rough endoplasmic reticulum protein p63. While it is not exclusively expressed on plasma cells, the presence of p63 distinguishes plasma cells from other lymphoid cells because of their high secretory activity.

A panel of antibodies for the immunostaining of Bouin's fixed bone marrow trephine biopsies

AIMS

To assess a panel of antibodies on Bouin's fixed bone marrow trephine (BMT) biopsies. These biopsies are widely used in routine diagnosis of various haematological malignancies and may be the sole material available in many centres; however, information regarding the immunostaining of this material is lacking.

METHODS

Biopsies were taken from 72 patients presenting with various haematological malignancies (leukaemia, 38; lymphoma, 14; multiple myeloma, 20). A panel of antibodies was assessed on Bouin's fixed BMT biopsies by the alkaline phosphatase-antialkaline phosphatase method.

RESULTS

Three B (MB2, LN-2, Ki-B5) and two T cell lineage antibodies (UCHL-1, CD3-r) reliably identified lymphoid cells, while MPO-r, Leu-M1/CD15, and KP-1/CD68 recognised cells from the myeloid or histiocytic/macrophage series. Reed-Sternberg cells were stained by LN-2, Leu-M1, and CD30. Antibodies specific for plasma cells (VS38) and hairy cells (DBA.44) gave a variable pattern of staining. Among the proliferation markers, proliferative cell nuclear antigen but not Ki-67 related antibodies were effective.

CONCLUSION

This study presents a panel of antibodies with reactivity not restricted to common fixatives that are also suitable for Bouin's fixed BMT biopsies.

Epstein-Barr virus (EBV) infection in infectious mononucleosis: virus latency, replication and phenotype of EBV-infected cells

Primary Epstein-Barr virus (EBV) infection may manifest itself as a benign lymphoproliferative disorder, infections mononucleosis (IM). EBV infection has been characterized in lymphoreticular tissues from nine patients with IM using the abundantly expressed EBV-encoded nuclear RNAs (EBERs) as a marker of latent infection. Expression of the virus-encoded nuclear antigen (EBNA) 2 and of the latent membrane protein (LMP) 1 was seen in variable proportions of cells in all cases. Double labelling revealed heterogeneous expression patterns of these proteins. Thus, in addition to cells revealing phenotypes consistent with latencies I (EBNA2-/LMP1-) and III (EBNA2+/LMP1+), cells displaying a latency II pattern (EBNA2-/LMP1+) were observed. Cells expressing EBNA2 but not LMP1 were also detected; whilst this may represent a transitory phenomenon, the exact significance of this observation is at present uncertain. EBER-specific in situ hybridization in conjunction with immunohistochemistry revealed expression of the EBERs mainly in B-lymphocytes, many of which showed features of plasma cell differentiation. By contrast, convincing evidence of latent EBV infection was not found in T-cells, epithelial or endothelial cells. Double-labelling immunohistochemistry revealed expression of the replication-associated BZLF1 protein in small lymphoid cells, often showing plasmacytoid differentiation. There was no unambiguous expression of this protein in other cell types. These results suggest that B-cells are the primary target of EBV infection and that plasma cells may be a source of infectious virus found in the saliva of IM patients.

A New Subtype of Large B-Cell Lymphoma Expressing the ALK Kinase and Lacking the 2; 5 Translocation

Seven cases of large B-cell lymphoma which define a previously unrecognized subgroup are reported. Morphologically they are comprised of monomorphic large immunoblast-like cells, containing large central nucleoli, which tend to invade lymphatic sinuses. Superficially they resemble anaplastic large cell lymphoma (ALCL) but they lack CD30. These lymphomas express epithelial membrane antigen (as do ALCL), but also contain intracytoplasmic IgA of a single light chain type (five cases) and an endoplasmic reticulum–associated marker detected by antibody VS38. They lack lineage-associated leukocyte antigens with the exception of CD4 (5 of 5 cases) and CD57 (5 of 7 cases). They are labeled by antibodies detecting both the intracytoplasmic and extracellular regions of the ALK receptor kinase, suggesting that they express the full-length form of this molecule. This was confirmed by Western blotting (in the one case tested) which showed a band of 200 kD in tumor cell lysates, and by polymerase chain reaction (PCR) amplification of mRNA encoding intracellular and extracellular ALK sequences (in the two cases tested). There was no evidence by cytogenetics (one case analyzed) or reverse transcriptase-PCR (three cases tested) of the 2; 5 translocation or the resultant NPM-ALK gene, as is commonly found in ALCL. All but one of the patients were male and all but one were adults, and in all but the latter case the disease followed an aggressive course.

A New Subtype of Large B-Cell Lymphoma Expressing the ALK Kinase and Lacking the 2; 5 Translocation

Seven cases of large B-cell lymphoma which define a previously unrecognized subgroup are reported. Morphologically they are comprised of monomorphic large immunoblast-like cells, containing large central nucleoli, which tend to invade lymphatic sinuses. Superficially they resemble anaplastic large cell lymphoma (ALCL) but they lack CD30. These lymphomas express epithelial membrane antigen (as do ALCL), but also contain intracytoplasmic IgA of a single light chain type (five cases) and an endoplasmic reticulum–associated marker detected by antibody VS38. They lack lineage-associated leukocyte antigens with the exception of CD4 (5 of 5 cases) and CD57 (5 of 7 cases). They are labeled by antibodies detecting both the intracytoplasmic and extracellular regions of the ALK receptor kinase, suggesting that they express the full-length form of this molecule. This was confirmed by Western blotting (in the one case tested) which showed a band of 200 kD in tumor cell lysates, and by polymerase chain reaction (PCR) amplification of mRNA encoding intracellular and extracellular ALK sequences (in the two cases tested). There was no evidence by cytogenetics (one case analyzed) or reverse transcriptase-PCR (three cases tested) of the 2; 5 translocation or the resultant NPM-ALK gene, as is commonly found in ALCL. All but one of the patients were male and all but one were adults, and in all but the latter case the disease followed an aggressive course.

VS38 immunostaining in melanocytic lesions

AIMS

To investigate the immunoreactivity of a range of melanocytic lesions, both benign and malignant, with the monoclonal antibody VS38. This was recently described as a marker of reactive/neoplastic plasma cells and, therefore, is useful in the diagnosis of plasmacytoma/myeloma and lymphomas with plasmacytic differentiation. This study was prompted by the recent observation that a plasmacytoid melanoma arising in the nasal cavity was strongly immunoreactive with VS38, which was therefore a potential source of major diagnostic error.

METHODS

The Streptavidin-peroxidase complex technique was used on paraffin wax embedded sections of 167 melanocytic lesions. Diaminobenzidine (DAB) was used as chromogen for non-pigmented or lightly pigmented lesions and nickel/DAB for more heavily pigmented lesions.

RESULTS

Positive immunostaining for VS38 was seen in 14.5% (10/69) of benign naevi (including 40% (four of 10) of Spitz naevi), 10.5% (two of 19) of dysplastic naevi/in situ melanomas, 92% (35/38) of primary cutaneous melanomas, 100% (four of four) of primary mucosal melanomas, 91.7% (33/36) of recurrent/metastatic melanomas, and 100% (one of one) of clear cell sarcomas of soft tissues.

CONCLUSIONS

VS38 immunostaining is frequently positive in primary and recurrent/metastatic malignant melanoma and is also reactive less commonly with benign naevi. These results should be borne in mind when this recently described marker of normal/neoplastic plasma cells is used to identify tumour lineage, particularly in tumours arising at unusual sites, such as in the nasal cavity. The possibility of malignant melanoma should be actively considered and excluded in any undifferentiated tumour which shows VS38 immunoreactivity.