Expression of costimulatory molecules in low-grade mucosa-associated lymphoid tissue-type lymphomas in vivo.

B-cell lymphomas of mucosa-associated lymphoid tissue (MALT) type develop against a background of chronic inflammation and have functional autoantigen receptors. Because they respond to environmental factors in vivo, the expression of costimulatory molecules, which play a key role in the differentiation of normal B-lymphocytes and in T-/B-cell interaction, may be critical in early MALT-type lymphoma pathogenesis until further chromosomal aberration leads to progression. We found a high number of tumor-infiltrating T-lymphocytes (TITLs) in all low-grade MALT-type lymphomas.