CD44 expression during tumor progression of follicular lymphoma.

Follicular lymphoma often progresses to diffuse type lymphoma. To elucidate the mechanisms of the diffuse evolution of follicular lymphoma, we investigated the expression pattern of CD44 in 28 cases of follicular lymphomas (FLs) using an immunohistochemical method and semi-quantitative PCR-Southern blot analysis. The FLs were divided into four groups: i) intrafollicular (IF); ii) infiltrative (INF); iii) partially follicular (PF); and iv) minimally follicular (MF), according to the histological classification by Lukes and Collins. Immunohistochemical analysis of CD44 using antibodies against CD44 common (CD44C) epitopes showed that CD44 was expressed in the diffuse area in the INF (0/8 cases), PF (12/12 cases), and MF (2/2 cases) lymphomas, whereas CD44 was not expressed in the lymphoma cells within the area of follicular growth of IF (0/6 cases) and INF (0/8 cases). Semi-quantitative PCR-Southern blot analysis showed that CD19-selected B cells from the FLs were expressed as a product of 482 base pairs (bp) corresponding to a CD44 standard form (CD44s) (5/5 cases). Additionally, the lymphoma cells from the PF were expressed as products of 600 and 1100 bp and the cells from MF were expressed as products of 600, 900, and 1100 bp with the CD44 exon 10 or 11 probes. The results indicated that the expression of CD44s and CD44 variants containing exon 10 and 11 were up-regulated according to the diffuse evolution of the follicular lymphoma.