Mono Mac 6 (MM6) is a human monocytic cell line commonly used as an in vitro model to demonstrate the actions of monocytes.
This cell line highly resembles mature blood monocytes. They have several similar features such as CD 14 antigen expression, phagocytotic ability, and the functional ability to produce cytokines. However, there still are some differences between Mono Mac 6 cells and human blood monocytes. A study that compares the production of cytokines by MM 6 cells in response to various stimulants to that of mature monocytes in peripheral blood mononuclear cells, shows that MM 6 cells lack the ability to express IFN-α. This cell line is a potent cytokine producer, with deficient capacity to produce IFN.
The development of in-vitro model systems advance the understanding of endothelial cell interactions and the adhesion properties of Mono Mac 6. It is proved that these cells show increased adherence to unstimulated and tumour necrosis factor (TNF)-α (50 U/ml), similar to freshly isolated human blood monocytes. And blocking experiments with monoclonal antibody directed against E-selectin, VCAM-1 and ICAM-1 on HUVEC and CD11b or CD14 on Mono Mac 6 cells demonstrate that these molecules all contribute to Mono Mac 6 adherence. What’s more, the study indicates that expression of CD11b and CD14 may also be responsible for the increased adhesion of Mono Mac 6. This property makes this cell line well suited for studying monocyte-endothelial cell interactions.
Application in Parallel Antimycobacterial Drug Studies
Several macrophage models have been used to test the intracellular activities of antituberculosis drugs, but there remains no fully differentiated human macrophage cell lines suitable for parallel use with murine cell lines. However, MM6 cells can make a useful model for testing the intracellular activities of antituberculosis drugs. Unlike the U937 and THP-1 human monocytic cell lines that must be induced to develop phagocytic properties, the MM6 has the ability to constitutively phagocytize antibody-coated erythrocytes and mycobacteria. Results of researches show that this cell line is very effective in determining the intracellular activities of antimycobacterial drugs.
Application in Developing In Vitro Assay Predictive of Adjuvant Safety in Vivo
There are many adjuvant formulations that are under development, but very few of them are licensed due to concerns about adverse side effects. Subunit vaccines composed of recombinant or purified antigens have a good safety record, but they are poorly immunogenic, requiring adjuvants to activate innate immunity and facilitate antigen specific immune response. The human Mono Mac 6 cell line exhibits many characteristics of mature blood monocytes including expression of the CD14 molecule and production of cytokines, such as interleukin-1 (IL-I), IL-6, and tumor necrosis factor, for which scientists have attempted to use it to develop in vitro assay predictive of adjuvant safety in vivo. This kind of developed human cell based assays will not only provide an important tool for early screening of new molecular moieties and adjuvant formulations but may assist in selection of safer products as well.