CD40LG and infection: According to the composition of immunoglobulins, cryoglobulins can be divided into three types: Type I, a monoclonal immunoglobulin (usually IgG or IgM, rarely IgA or free light chain) that can be seen in malignant tumors with B cell lineage; Type II, which is a mixed type of monoclonal IgM and polyclonal IgG that can be seen in hepatitis C and other infections, connective tissue diseases (CTDs) and lymphoproliferative diseases; Type III, which is polyclonal IgM and polyclonal IgG, and usually appears secondary to CTDs or infection.