Regulated adherence of monocytes to extracellular matrix macromolecules is a prerequisite for their accumulation at sites of pulmonary infection and inflammation. To begin to assess the pathobiological importance of alterations in monocyte adherence to extracellular matrix in inflammatory lung diseases, the adherence properties of monocytes from patients with an inflammatory lung disease (bronchiectasis) and healthy subjects to a representative matrix component (fibronectin) were compared. Spontaneous adherence of monocytes from the control subjects was 20 to 25%, whereas that of the patients' cells was 2 to 3-fold higher and correlated with the severity of airway inflammation. Endotoxin (LPS) and cytokines from areas of airway disease are likely to be responsible for the observed monocyte activation since: 1) LPS was detected in plasma from all of the patients but none of the control subjects; and 2) LPS and cytokines produced dose-related increases in the adherence of normal monocytes in vitro. Monocyte adherence to fibronectin was substantially mediated by CD11/CD18 integrins, via both RGD-dependent and RGD-independent mechanisms. These data indicate that signals arising from foci of pulmonary inflammation are likely determinants of the accumulation of monocytes in the lungs of patients with chronic inflammatory lung diseases. There was a striking relationship between the adherence properties of monocytes and functions that are of biological importance at sites of inflammation. Spontaneously adherent monocytes had an "inflammatory effector" phenotype, non-adherent cells had an "immune modulatory" phenotype and monocytes that could stimulated to adhere by LPS (LPS-adherent cells) had an intermediate phenotype. In addition, only the adherent monocyte subpopulations were replete with HLE and these cells contained a substantial (10 to 11-fold) molar excess of HLE compared with the physiological inhibitor of this enzyme (a1-antitrypsin). Maturation in vitro increased the accumulation of a1-antitrypsin by all of the monocyte subpopulations. In contrast, proinflammatory mediators up-regulated a1-antitrypsin accumulation by only the spontaneously adherent cells, probably by translational or post-translational mechanisms. In conclusion, these data indicate that monocytes are heterogeneous in their ability to accumulate at sites of infection and inflammation. In addition, the capacity of monocytes to adhere to fibronectin is related to monocyte functions that are of biological importance at sites of infection and inflammation. Furthermore, LPS released from foci of infection, may induce the accumulation of monocytes with an inflammatory effector phenotype, and may thereby promote resolution of tissue infection. Alternatively, LPS may promote the recruitment of monocytes with capacity to contribute to HLE-mediated tissue injury.

Fibrocytes are monocyte-derived cells that morphologically look like fibroblasts, express both stromal and haematopoietic markers, and have been reported as being involved in wound healing and fibrosis. In-vitro derived fibrocytes can be differentiated in both serum-containing and serum-free environments and we wanted to study the relationship between these two fibrocytes; which potentially could be involved at different time points at a wound healing site. To investigate the relationship between serum-free and serum-containing derived fibrocytes monocytes were differentiated without serum. When these cells were placed in a serum-containing environment they became round, losing their fibroblast-like morphology. However when the reverse experiment was done on fibrocytes derived in a serum-containing environment there was no apparent effect on their morphology. The relationships between these two fibrocytes, as well as macrophages and fibroblasts was also examined using transcriptome analysis of 37000 genes, clustering the samples based on all the genes, and identifying those that were significantly different between the populations. This demonstrated that both fibrocyte populations are distinct from each other, as well as from both fibroblasts and macrophages. These data demonstrate that these two fibrocytes have different characteristics, suggesting that they may have different roles in the modulation of fibrosis in inflammation.

This thesis investigated the effect of acute psychological stress and \(\beta\)-adrenergic receptor (\(\beta\)AR) stimulation on the mobilization of CD8+ T lymphocytes (CD8TLs) and progenitor cell (PC) populations. Chapter 2 demonstrated that CD8TL stress- and \(\beta\)AR- sensitivity increases in parallel with greater effector functions and cell differentiation. As Cytomegalovirus (CMV) infection influences CD8TL differentiation, Chapter 3 compared the mobilization of cytotoxic lymphocytes in CMV seropositive and seronegative individuals; CMV infection enhanced the stress reactivity of CD8TLs, CD4TLs and NKT-like cells. Chapter 4 examined whether antigen-specificity could modulate CD8TL stress- and \(\beta\)AR-sensitivity. CMV-specific cells demonstrated enhanced mobilization compared to the total-memory CD8TL and the total Epstein-Barr virus (EBV) population. In Chapter 5, we demonstrated that PC subsets, capable of both replenishing leukocyte populations and maintaining endothelial integrity, were also mobilized by acute psychological stress. This result was not replicated by \(\beta\)ARagonist infusion suggesting the involvement of \(\alpha\)AR or non-adrenergic mechanism. In sum, the current findings suggest that stress mobilization serves to protect the host by increasing immune protection and tissue repair mechanisms. However, such a response may also be detrimental dependent on the circumstance, i.e., infection versus inflammation.

Rodent hepatic myofibroblasts are susceptible to nerve growth factor-mediated apoptosis through p75 neurotrophin receptor ligation. Hepatic myofibroblast apoptosis is critical to resolution of liver fibrosis. I show that human hepatic myofibroblasts exhibit differential responses to mature and pro-nerve growth factor/p75 neurotrophin receptor-mediated signals. Whilst mature nerve growth factor is proapoptotic, pronerve growth factor protects human hepatic myofibroblasts from serum-deprivation and cycloheximide-induced apoptosis. To define the dominant effect of p75 neurotrophin receptor-mediated events in experimental liver fibrosis I have used a mouse lacking the p75 neurotrophin receptor ligand-binding domain but expressing the intracellular domain. I show that absence of p75 neurotrophin receptor ligand-mediated signals leads to significantly retarded architectural resolution and reduced hepatic myofibroblast loss by apoptosis. Lack of the ligand-competent p75 neurotrophin receptor limits hepatocyte proliferative capacity in vivo without preventing hepatic stellate cell transdifferentiation. Moreover, in recovery from experimental liver fibrosis the fall in pro-nerve growth factor mirrors loss of hepatic myofibroblasts by apoptosis. Thus, nerve growth factor species have a differential effect on hepatic myofibroblast survival, and p75 neurotrophin receptor ligand-mediated events facilitate reduction of liver fibrosis via regulation of hepatic myofibroblast proliferation and apoptosis, and hepatocyte proliferation.