Independent expression of the two paralogous CCL4 genes in monocytes and B lymphocytes

The CCL4 chemokine is secreted by a variety of cells following stimulation. CCL4 affects several different types of cells that are important for acute inflammatory responses and are critical for the development of specific immune responses to foreign antigens. The human genome contains two genes for the CCL4 chemokine. Although highly homologous, the two genes encode slightly different proteins. We analyzed the mRNA expressed in monocytes and B lymphocytes and found that while monocytes express predominantly one CCL4 gene, known as ACT-2, peripheral blood B lymphocytes express a mixture of ACT-2 and the second CCL4 gene, lymphocyte activating gene-1 ( LAG-1). Although peripheral blood B cells, CD27(-) B cells, and CD27(+) B cells all express a mixture of LAG-1 and ACT-2, the B-cell lines that were studied regulate the two genes independently. RL, SU-DHL-6, and REH cells predominantly express LAG-1. These studies demonstrate that monocytes and B cells utilize different mechanisms to regulate expression of the two CCL4 genes and suggest that the two genes may not have identical activities.