Bone marrow B-cell clonal expansion in type II mixed cryoglobulinaemia: association with nephritis

To investigate the relationship between the pattern of bone marrow (BM) B-cell expansion and the clinical features of mixed cryoglobulinaemia (MC) syndrome.

Fifty-five patients with type II MC syndrome were analysed. Their median age was 64 yrs (range 24-82), the median disease duration was 6 yrs (range 1-26) and the mean follow-up after BM analysis was 2.65 yrs (s.d. = 1.33). Peripheral neuropathy was present in 33 patients (60%), nephritis in 14 (25.4%), skin ulcers in 14 (25.4%) and lymphoma or atypical lymphoproliferative disorder (LPD) in 17/55 (30.9%). Anti-HCV antibodies were found in 43/55 patients (78.2%). BM B-cell expansion was evaluated by a semi-nested PCR amplification of the V-D-J region of the IgH genes.

A clonal B-cell expansion in the BM was found in 33/55 (60%) patients, while a polyclonal pattern in 22/55 (40%). A BM pattern of clonal B-cell expansion increased the risk of nephritis of about 10 times [odds ratio (OR) = 10.11, CI95%1.52-67.31], if compared to a polyclonal pattern. In contrast, the risk of skin ulcers was decreased in BM clonal cases (OR = 0.09, CI95%0.02-0.49). Overt lymphomas did not emerge from patients with BM monoclonal expansion (without clinical or histopathological features of lymphoproliferation; or with LPD) in a short-term, consistent with the finding that monoclonality was associated with nephritis and not with an underlying, not recognized lymphoma.

BM clonal B-cell expansion is associated with nephritis in MC syndrome. Particular B-cell clones may be preferentially expanded and may play a pathogenic role in MC nephritis.