Possible mechanisms for the elevation of serum beta 2-microglobulin levels in adult T-cell leukemia.

: In our previous study, we found that serum beta 2-microglobulin (beta 2M) levels were elevated in the active, but not in the inactive, phase of adult T-cell leukemia (ATL), suggesting a correlation between the beta 2M level and the clinical severity of this disease. In this study we examined the mechanisms underlying the elevation of serum beta 2M levels in ATL. First, the production of beta 2M by ATL cells was investigated in vitro. High levels of beta 2M were detected in the conditioned culture medium (CM) of ATL cells from seven out of nine patients. Second, we assessed the effects of the CM on the release of beta 2M by three human cell lines unrelated to ATL (NCTC 2544, Chang liver, and L 132; originating from the skin, the liver, and the fetal lung, respectively). Most of the CM definitely promoted beta 2M production by these cell lines. beta 2M production by the cell lines was markedly promoted by exogenous interferon-gamma (IFN-gamma), a well-known potent inducer of class I HLA antigen expression. We then investigated whether an antibody directed against IFN-gamma could attenuate the activity of three ATL CM. The anti-IFN-gamma antibody reduced the stimulatory activity of the CM to 28-65% of the original level, but did not affect basal beta 2M production by these cell lines. These data suggest that there are at least two mechanisms causing the elevation of serum beta 2M levels in ATL; direct production by tumor cells, and production by non-malignant cells that is mediated via humoral factors secreted by the ATL cells.(ABSTRACT TRUNCATED AT 250 WORDS)