Matrix metalloproteinases (MMPs) are zinc-dependent endopeptidases that are a subfamily of metzincins. Matrix metalloproteinases are responsible for much of the turnover of extra-cellular matrix components and are key to a wide range of processes including tissue remodeling and release of biological factors. Imbalance between the MMPs and endogenous tissue inhibitors of metalloproteinases (TIMPs) can result in dysregulation of many biologic processes and lead to the development of malignancy, cardiovascular disease, and autoimmune and inflammatory disorders. MMP production by monocyte/macrophages is dependent on the cell type, state of differentiation, and/or level of activation and whether they are infected, e.g., by HIV-1. MMP expression by HIV-1 infected monocytes and macrophages may alter cellular trafficking and contribute to HIV-associated pathology such as HIV-associated dementia (HAD). This review will provide a classification of the MMP super-family with particular reference to those produced by monocyte/macrophages, describe their regulation and function within the immune system, and indicate their possible roles in the pathogenesis of disease, including HIV-associated dementia.

The catabolic pathway of L-tryptophan (L-trp), known as the kynurenine pathway (KP), has been implicated in the pathogenesis of a wide range of brain diseases through its ability to lead to immune tolerance and neurotoxicity. As endothelial cells (ECs) and pericytes of the blood-brain-barrier (BBB) are among the first brain-associated cells that a blood-borne pathogen would encounter, we sought to determine their expression of the KP. Using RT-PCR and HPLC/GC-MS, we show that BBB ECs and pericytes constitutively express components of the KP. BBB ECs constitutively synthesized kynurenic acid, and after immune activation, kynurenine (KYN), which is secreted basolaterally. BBB pericytes produced small amounts of picolinic acid and after immune activation, KYN. These results have significant implications for the pathogenesis of inflammatory brain diseases in general, particularly human immunodeficiency virus (HIV)-related brain disease. Kynurenine pathway activation at the BBB results in local immune tolerance and neurotoxicity: the basolateral secretion of excess KYN can be further metabolized by perivascular macrophages and microglia with synthesis of quinolinic acid. The results point to a mechanism whereby a systemic inflammatory signal can be transduced across an intact BBB to cause local neurotoxicity.

Migration of monocytes from the bloodstream across vascular endothelium is required for routine immunological surveillance of tissues and their entry into inflamed sites. Transendothelial migration of monocytes initially involves tethering of cells to the endothelium, followed by loose rolling along the vascular surface, firm adhesion to the endothelium and diapedesis between the tightly apposing endothelial cells. A number of adhesion molecules are involved in this process. Monocyte rolling can be mediated by selectins and their ligands, or alpha(4)beta(1) integrin interacting with endothelial VCAM-1. On the apical surface of the endothelial cell, bound chemokines (eg. MCP-1, MIP-1alpha/beta) can activate leukocyte beta(2) integrins for tight adhesion to ICAM-1 and -2. Diapedesis by monocytes occurs through interaction between PECAM-1 on both the monocyte and the endothelial cells, followed by similar homophilic adhesion via CD99. After penetration of the endothelial basement membrane, monocytes migrate through the extracellular matrix of the tissues where they may differentiate into tissue macrophages and/or migrate to sites of inflammation. Additionally, monocytes in the tissues may traffic to the lymphatics or back into the bloodstream, both of which involve basal to apical (reverse) transendothelial migration, possibly mediated by tissue factor and p-glycoprotein. Monocyte trafficking is of current interest in studies of the pathogenesis of HIV-infection, including establishment of viral reservoirs in tissues and sanctuary sites and the development of HIV-related dementia. This review provides insights into the most recent studies on the process of monocyte migration across the vascular endothelium, and changes in migration that can occur during HIV-infection.

Multi-gene transgenic pigs would be of benefit for large animal models in medical, agricultural, and pharmaceutical applications; in particular for xenotransplantation, where extensive genetic manipulation of donor pigs is required to make them suitable for organ grafting to humans. We used the sperm mediated gene transfer (SMGT) method to produce with high efficiency multi-gene transgenic pigs using three genes coding for fluorescent proteins: enhanced blue (EBFP), green (EGFP), and red (DsRed2). All three fluorescent proteins were expressed in 171 out of 195 normally developed morula/blastocysts examined at day 6 post insemination (88%). Genomic DNA of 18 piglets born from two litters was screened by PCR, showing that all piglets were transgenic with at least one gene, 7/18 piglets were triple transgenic, 7/18 double transgenic, and 4/18 single transgenic. Fluorescence in situ hybridization (FISH) analysis revealed multiple sites of integration of the transgenes. RNA and protein expression was found in muscle, heart, liver, hair, and peripheral blood mononuclear cells (PBMCs). These results show that SMGT is an effective method for introducing multiple genes into pigs as shown by the simultaneous expression of three fluorescent proteins.