An investigation into sex-differences in the regulation and function of Toll-like receptors in leukocyte trafficking in vivo

Abstract

Sexual dimorphisms exist in the incidence and severity of many diseases, with females demonstrating relative protection from inflammatory conditions. The extent and mechanisms by which excessive leukocyte recruitment underlies these differences are not well established, and better understanding is essential for the development of targeted therapies. Evidence suggests that variances in pathogen-sensing Toll-like receptors (TLRs) underlie sex-differences in leukocyte recruitment. This thesis aimed to investigate sex-differences in trafficking of leukocytes in the zymosan peritonitis murine model of acute inflammation and furthermore evaluate if these differences were accompanied by changes in TLR2 or TLR4 expression. This work shows that female mice recruit fewer classical monocytes and neutrophils during zymosan induced peritonitis. It demonstrates female murine peritoneal macrophages are more numerous, whilst the peritoneal cytokine environments and zymosan-sensing receptors are similar between the sexes. Sex-differences were evident in the circulation as female mice showed reduced neutrophilia and monocytosis versus male counterparts, despite having similar mobilisation from bone marrow (BM) stores. The work further revealed that storage and trafficking of splenic leukocytes during acute inflammation is distinct between the sexes. Male mice have greater splenic stores of neutrophils, classical- and non-classical- monocytes, despite similar spleen sizes, signifying another source of potential pathogenic leukocytes. Furthermore, males but not females mobilise splenic classical monocytes in response to peritonitis. Conversely, neutrophils appear to traffic to the spleen in females, but not males, in this model. Whilst BM neutrophils from males displayed more TLR2 and TLR4 than females, no major differences under basal or inflamed conditions in TLR2 or TLR4 expression were evident on leukocyte subsets. This work demonstrates that males and females have distinct leukocyte trafficking profiles in acute inflammation, and suggests that the spleen, not the BM, plays a role in determining sex-differences in the available pool of immune cells. Such dimorphisms demonstrate the importance of considering gender in assay development, drug design and clinical trials.