The role of Toll-like receptor mediated signalling in the pathogenesis of multiple myeloma

Toll-like receptors are critical structures in sensing the invading pathogens via conserved moieties termed pathogen associated molecular patterns and in directing the innate and adaptive immune responses. Studies have shown that Toll-like receptors are not limited to normal immune cells but are expressed on tumour cells as well, including those of lymphoid neoplasms particularly B-cell malignancies, multiple myeloma and chronic lymphocytic leukemia. Neoplastic plasma cells in multiple myeloma usually show a different pattern of Toll-like receptor expression compared to normal B cells. These receptors on multiple myeloma cells, have been indicated to have a role in their proliferation, differentiation and survival, probably through induction of autocrine IL-6 secretion, and in their immunomodulatory functions. Moreover, it is speculated that these molecules may contribute to osteolytic lesions through activation of osteoclasts, and to angiogenesis through induction of pro-angiogenic factors. Knowledge on Toll-like receptor signalling in the biology of malignant plasma cells or their cellular microenvironment may give new insights into pathogenesis of multiple myeloma and may open new avenues for the therapy of this disease.