The respiratory burst of immune cells is an integral part of host defense. In this study, we investigate the effect of temperature (between 25°C and 42°C) on the dynamics of superoxide (O2-) production during the respiratory burst in PMA-activated THP-1 monocytes.
The dynamics of superoxide production of PMA-activated monocytes is measured at each temperature (between 25°C and 42°C) as the superoxide dismutase-inhibitable reduction of cytochrome c using the classical spectrophotometric assay.
At each temperature, the cumulative O2- concentration shows a lag period with low O2- production, followed by a period of accelerated production and then a slow saturation to a steady state concentration. Our measurements show that both the dynamics of O2- production and the maximum amount of O2- produced at steady state are affected by temperature, with the latter being affected more profoundly. The steady state O2- concentration shows a triphasic response with respect to temperature –an initial period of gradual increase between 25°C and 32°C is followed by a period of sharp rise in steady state concentration between 32°C and 37°C, and subsequently a fast monotonic decrease when temperature exceeds 37°C.
The observed rate of O2- production is proportional to the intracellular concentration of the fully-assembled activated membrane-bound enzyme NADPH oxidase (NOX). Based on our mathematical model, we speculate that between 25°C and 32°C, the assembly of NOX occurs in the transport limited regime, the rate of which increases weakly with temperature. For temperatures between 32°C and 37°C, the activation of NOX occurs in the kinetically controlled regime and thus increases rapidly with temperature. At temperatures above 37°C, the assembled NOX deactivates and/or internalizes rapidly, leading to a fast monotonic decrease of steady state O2-concentration with increasing temperature.
Hypothermia has been advocated as a means to minimize ischemia reperfusion injury as might occur cerebro-vascular accidents and acute myocardial infarction. Our results indicate that hypothermia (as well as fever) could lead to a depression of immune cell function.
Victor Salloum, None.