Microcalorimetry does not predict the cellular phagocytosis of latex microspheres

Current literature highlights the potential suitability of microcalorimetry for the investigation of cell-drug interactions. Previous work using bacte ria or antigens derived from infectious organisms yielded conclusions that heat production is a quantitative means of measuring phagocytosis, In this study we evaluated the potential of flow-through microcalorimetry as a meth od of quantifying the phagocytosis of microsphere particulates. The techniq ue avoids the need to incorporate radioactive or fluorescent markers into t he particulate formulation, and would be widely applicable in biopharmaceut ical research. Using the monocyte cell line Mono Mac 6 a power output of 9. 00 mu W per million cells was increased significantly on addition of zymosa n, lipopolysaccaride (LPS) and phorbol myristate acetate but not following exposure to FITC labelled latex microspheres (LM). TNF alpha production inc reased on exposure to zymosan, LPS and LPS-phorbol myristate acetate, thoug h not on exposure to LB. An assay was developed which allowed the quantific ation of internalised particulates in phagocytic cells using fluorescent ac tivated cell sorting (FACS). In contrast to the microcalorimetric and TNF a lpha data FAGS revealed that 20% of the MM6 population phagocytosed a mean of 1.35 LM. Microcalorimetry and measurements of TNF alpha. production are assays of cellular activation a phenomenon not necessarily associated with phagocytosis. FAGS, however, serves as a specific and quantitative measure of phagocytosis. Microcalorimetry may not be a suitable technique for the q uantitative assessment of the phagocytosis of drug delivery particulates. ( C) 2000 Elsevier Science B.V. All rights reserved.