Abstract
Among recently discovered B cell activators responsible for signaling events leading to B-cell activation and maturation, of particular interest are the Toll-like receptors (TLRs). TLR expression is heterogeneous and variable among B-cells. In addition, abnormal TLR levels/signaling may play an important role in the pathogenesis of lymphoma, particularly in splenic marginal zone lymphoma (SMZL), since TLR pathways are recurrently targeted by genetic changes in this lymphoma.
Frozen spleen tissue specimens from patients with SMZL (n=13) and splenic diffuse red pulp lymphoma with villous lymphocytes (SDRPL, n=5) were analyzed for the expression of TLR1 to TLR10 in comparison to control cases (traumatic spleen, n=7) using multi-parametric flow cytometry and quantitative mRNA Taqman assay. To identify the B-cell subset, the samples were also stained with anti-CD19 and anti-CD3. All cases were studied by morphological, immunological, cytogenetic and molecular analysis.
The TLR profile obtained at protein level by flow cytometry was closely related to that obtained at mRNA level. The SMZL/SDRPL B-cells expressed all TLRs, but with variable levels of protein expression (low for TLR1, TLR2, TLR3, TLR8, TLR9, TLR10, and high for TLR4, TLR5, TLR6 and TLR7). On the other hand, distinct TLRs profiles were observed according lymphoma subtypes. The SDRPL cases showed indeed a significant TLR2 under-expression and TLR4/TLR7 over-expression in comparison to SMZL cases and control B-cells. SMZL cases exhibited a significant TLR4/TLR8 over-expression in comparison to control B-cells. These TLR profiles were not associated with specific cytogenetic features (presence of del7q or trisomy 3) and/or immunological profile (expression of the CD11c/CD27/isotype of immunoglobulin). But, in both entities, TLR4 expression was higher in cases with mutated IGHV than in cases with unmutated IGHV. The overexpression of TLR7 MyD88-dependent signaling molecules has been reported as pathogenic mechanism for autoimmune diseases; however no more autoimmune disease or circulating auto-antibodies were associated with SDRPL cases as compared to SMZL cases. As previously reported, all cases but one SMZL case presented unmutated MyD88 (L265P mutation), and MyD88 protein evaluated here by flow cytometry was similarly expressed in both entities. While TLR7 stimulation is known to induce CD38 expression, all SDRPL cases were CD38 negative; while in SMZL cases, higher TLR7 expression was observed in CD38 positive as compared to CD38-negative cases. This may suggest the existence of an abnormal TLR7 pathway in SDRPL as opposed to SMZL.
TLR profiling should allow a better understanding of the mechanisms involved in SMZL/SDRPL pathogenesis. Present data suggest an abnormal TLR pathway involving NF-kB and/or MyD88 in the SDRPL entities.
No relevant conflicts of interest to declare.
Author notes
Asterisk with author names denotes non-ASH members.
