Human B lymphocytes can produce leukotriene B₄ but the biological function of the 5-lipoxygenase (5-LO) pathway in B cells is unclear. In order to better understand and define the role of 5-LO in B cells, we investigated the expression of 5-LO mRNA and protein in subsets of B cells from human tonsils and different types of B cell lymphoma.

Based on RT-PCR and western blot/immunohistochemical staining, with a polyclonal antibody raised against 5-LO, high expression of 5-LO was found in mantle zone B cells from tonsils. By contrast, only a weak expression of 5-LO was detected in germinal centre cells and no expression in plasma cells from tonsils. This pattern of 5-LO expression was preserved in malignant lymphoma with high expression in mantle B cell lymphoma (MCL) and weak or no expression in follicular lymphoma. Primary leukemized MCL, so called B-prolymphocytic leukaemia cells, and MCL cell lines also expressed 5-LO and readily produced LTB₄ after activation.

The present report demonstrates the expression of 5-LO mainly in normal and malignant mantle zone B cells while the expression is low or absent in germinal centre B cells and plasma cells, indicating a role of the 5-LO pathway in B cells before the cells finally differentiate to plasma cells.