The effects of physical activity level, sex, and different exercise protocols on monocyte TLR expression

It has been suggested that moderate exercise contributes to protection against the development of chronic diseases by anti-inflammatory mechanisms that include elevations of anti-inflammatory cytokines and also reduction of the expression of Toll- Like Receptors (TLRs). However, prolonged strenuous exercise has been shown to reduce the function of some immune cells, decrease virus protection and consequently may account for the reason athletes appear more vulnerable to catching Upper Respiratory Tract Infections (URTI). Although it has been proven that some exercise is better than no exercise, it is not clear yet what is the right amount of exercise to elicit beneficial immune responses and to help prevent the development of diseases. Therefore, the general aim of the studies in this thesis was to evaluate the impact of different types of exercise on monocyte TLR expression in participants with different fitness levels. It was found that different acute exercise protocols elicit different changes in TLR2 and TLR4 expression, where an acute bout of strenuous exercise reduced TLR4 expression for a few hours after the completion of the exercise (Chapter 5); however, short two bouts of exhaustive exercise separated by 2 hours did not change TLR4 expression (Chapter 6). In addition, changes in TLR4 expression were related to sex and the physical activity level of the participants (Chapter 4), and should therefore be considered separately when analysing TLR4 expression. Furthermore, high-intensity intermittent training improves participants’ aerobic capacity and modifies the monocyte subpopulation concentration in the blood, with no changes in TLR4 expression. Further research needs to be done in this area to achieve a conclusive finding about changes in TLR4 expression and monocyte subsets after different training protocols, and possible relationships to cytokine production.