MALT B cell lymphomas with t(1;14)(p22;q32) showed a recurrent breakpoint upstream of the promoter of a novel gene, Bcl10. Bcl10 is a cellular homolog of the equine herpesvirus-2 E10 gene: both contain an amino-terminal caspase recruitment domain (CARD) homologous to that found in several apoptotic molecules. Bcl10 and E10 activated NF-kappaB but caused apoptosis of 293 cells. Bcl10 expressed in a MALT lymphoma exhibited a frameshift mutation resulting in truncation distal to the CARD. Truncated Bcl10 activated NF-kappaB but did not induce apoptosis. Wild-type Bcl10 suppressed transformation, whereas mutant forms had lost this activity and displayed gain-of-function transforming activity. Similar mutations were detected in other tumor types, indicating that Bcl10 may be commonly involved in the pathogenesis of human malignancy.

Detection of B-cell monoclonality using the polymerase chain reaction (PCR) promises the quick and cost-effective separation of monoclonal from polyclonal B-cell disease. However, the efficiency of the method has yet to be fully assessed, particularly with regard to disease type and selection of PCR primers. We have evaluated two approaches based on amplification of the immunoglobulin heavy chain gene using framework 2 (Fr2) and framework 3 (Fr3) region primers. Frozen tissue samples from 94 cases of low-grade B-cell lymphoma were investigated, all of which had previously been shown to be monoclonal by Southern blot analysis. Using a Fr2 primer, we were able to show monoclonality in 85 per cent of cases; with Fr3, 80 per cent of cases; and using both techniques in separate reactions, 90 per cent of cases. Thus, a significant false-negative rate exists with either primer which can be reduced by using both. We also found a difference in the efficiency of detection in different types of lymphoma; only 87 per cent of mucosa-associated lymphomas and centroblastic/centrocytic lymphomas were shown to be monoclonal, whereas all of the other lymphoma types tested were positive using one or both methods. We conclude that PCR detection of B-cell monoclonality allows rapid analysis of tissue samples, including paraffin-processed material. False-negative results which occur in some types of lymphoma can be reduced by the use of two or more primer combinations.

High-grade MALT lymphomas often contain low-grade tumour components; both cell populations have been shown to express the same immunoglobulin light chain previously. However, the clonal link between the low and high-grade components has not been established at the genetic level. To investigate this link, we have examined low- and high-grade components micro-dissected from tissue sections of four high-grade gastric MALT lymphomas. PCR and sequence analyses were performed to identify clone-specific rearranged immunoglobulin heavy chain gene sequences. In each of these cases, the PCR products from the two components were identical in size by electrophoresis. Direct sequencing revealed common clone-specific immunoglobulin heavy chain gene rearrangements in both lesions of each case, providing genetic evidence for a clonal link. These results support the proposal that high-grade MALT lymphomas generally evolve from low-grade clones.

The genetic mechanisms underlying the genesis of low-grade mucosa- associated lymphoid tissue (MALT) lymphomas and their transformation into high-grade lymphoma are poorly understood. p53 inactivation, commonly caused by mutation and allele loss, has been shown to play an important role in the early development and/or the late disease progression of many human tumors including lymphoid malignancies and, thus, may also be important in MALT lymphomagenesis. We examined 75 cases (48 low grade and 27 high grade) of MALT lymphoma for p53 allele loss and mutation as well as protein accumulation. DNA samples prepared from microdissected cell populations were used for the detection of p53 gene abnormalities. Loss of heterozygosity (LOH) of the gene was detected by polymerase chain reaction-based analysis of p53 CA repeat polymorphism, whereas p53 mutation was studied by single-strand conformation polymorphism analysis and direct sequencing. p53 expression was assessed by immunostaining with CM1 polyclonal antibody. p53 allele loss and mutation, which resulted in the alteration in the amino acid sequence, were found in both low-grade (LOH, 3 of 44 [6.8%]; mutation, 9 of 48 [18.8%]) and high-grade (LOH, 6 of 21 [28.6%]; mutation, 9 of 27 [33.3%]) MALT lymphomas, particularly in the latter group. p53 staining was not observed in any low-grade tumors but in 6 high-grade cases that harbored missense mutations. There were also differences in the extent of p53 abnormalities, between low- and high- grade tumors. Of the 11 low-grade tumors showing p53 abnormalities, only 1 tumor showed the concomitance of p53 mutation and allele loss, whereas in high-grade tumors, 6 of 9 affected cases displayed both p53 mutation and allele loss. Our results suggest that p53 partial inactivation may play an important role in the development of low-grade MALT lymphomas, whereas complete inactivation may be associated with high-grade transformation.

Aims-To evaluate the polymerase chain reaction (PCR) demonstration of clonal immunoglobulin heavy chain gene rearrangements using routinely prepared,