Inhibition of microglia multinucleated giant cell formation and induction of differentiation by GM-CSF using a porcine in vitro model

Differential regulation of microglial states by colony stimulating factors

Recent studies have emphasized the role of microglia in the progression of many neurodegenerative diseases. The colony stimulating factors, CSF-1 (M-CSF), granulocyte-macrophage CSF (GM-CSF) and granulocyte CSF (G-CSF) regulate microglia through different cognate receptors. While the receptors for GM-CSF (GM-CSFR) and G-CSF (G-CSFR) are specific for their ligands, CSF-1 shares its receptor, the CSF-1 receptor-tyrosine kinase (CSF-1R), with interleukin-34 (IL-34). All four cytokines are expressed locally in the CNS. Activation of the CSF-1R in macrophages is anti-inflammatory. In contrast, the actions of GM-CSF and G-CSF elicit different activated states. We here review the roles of each of these cytokines in the CNS and how they contribute to the development of disease in a mouse model of CSF-1R-related leukodystrophy. Understanding their roles in this model may illuminate their contribution to the development or exacerbation of other neurodegenerative diseases.

Roles of CSF2 as a modulator of inflammation during retinal degeneration

Colony-stimulating factor 2 (CSF2) is a potent cytokine that stimulates myeloid cells, such as dendritic cells and macrophages. We have been analyzing the roles of microglia in retinal degeneration through the modulation of inflammation in the eye, and examined the roles of CSF2 in this process. Both subunits of the CSF2 receptor are expressed in microglia, but no evidence suggesting the involvement of CSF2 in inflammation in the degenerating eye has been reported. We found that Csf2 transcripts were induced in the early phase of in vitro mouse adult retina culture, used as degeneration models, suggesting that CSF2 induction is one of the earliest events occurring in the pathology of retinal degeneration. The administration of CSF2 into the retina after systemic NaIO₃ treatment increased the number of microglia. To examine the roles of CSF2 in retinal inflammation, we overexpressed CSF2 in retinal explants. Induction of CSF2 activated microglia and Müller glia, and the layer structure of the retina was severely perturbed. CC motif chemokine ligand 2 (Ccl2) and C-X-C motif chemokine ligand 10 (Cxcl10), both of which are expressed in activated microglia, were strongly induced by the expression of CSF2 in the retina. The addition of CSF2 to primary retinal microglia and the microglial cell lines MG5 and BV2 showed statistically significant increase in Ccl2 and Il1b transcripts. Furthermore, CSF2 induced proliferation, migration, and phagocytosis in MG5 and/or BV2. The effects of CSF2 on microglia were mild, suggesting that CSF2 induced strong inflammation in the context of the retinal environment.

Colony stimulating factors in the nervous system

Although traditionally seen as regulators of hematopoiesis, colony-stimulating factors (CSFs) have emerged as important players in the nervous system, both in health and disease. This review summarizes the cellular sources, patterns of expression and physiological roles of the macrophage (CSF-1, IL-34), granulocyte-macrophage (GM-CSF) and granulocyte (G-CSF) colony stimulating factors within the nervous system, with a particular focus on their actions on microglia. CSF-1 and IL-34, via the CSF-1R, are required for the development, proliferation and maintenance of essentially all CNS microglia in a temporal and regional specific manner. In contrast, in steady state, GM-CSF and G-CSF are mainly involved in regulation of microglial function. The alterations in expression of these growth factors and their receptors, that have been reported in several neurological diseases, are described and the outcomes of their therapeutic targeting in mouse models and humans are discussed.

A modified protocol for isolation of retinal microglia from the pig

Microglia are the resident immune cells in the retina. To investigate their properties and behaviour, a reliable and yielding procedure to culture them is necessary. We here describe a way of isolation of microglial cells from the porcine retina, as pig eyes are similar to human eyes in size, structure and vasculature, including similarities in proteins and pathways. Retina was isolated from fresh pig eyes, dissociated by a mixture of collagenase, hyaluronidase and DNAse, and passed through a cell strainer. After triple centrifugation with decreasing velocity and re-suspension, cells were seeded into poly-d-lysine coated culture flasks and cultured using DMEM and macrophage-colony stimulating factor (M-CSF). Number of cells increased gradually during the first 10-14 days, till they could be split and used for experiments. Identity of isolated cells as microglia was assessed by immunostaining against the microglia/macrophage markers Iba1, CD11b, CD68, CD45 and TMEM119. Phagocytic function of microglia could be demonstrated by phagocytosis of fluorescence beads and their response to lipopolysaccharide (LPS). As a conclusion, we developed a protocol for isolation and cultivation of pig retinal microglial cells that are suitable for research in the laboratory.

Rapid Proteome Changes in Plasma and Cerebrospinal Fluid Following Bacterial Infection in Preterm Newborn Pigs

Background: Neonatal infection and sepsis are common for preterm infants due to their immature immune system. Early diagnosis is important for effective treatment, but few early markers of systemic and neuro-inflammatory responses in neonates are known. We hypothesised that systemic infection with Staphylococcus epidermidis (SE), a Gram-positive bacteria, induces acute changes to proteins in the plasma and cerebrospinal fluid (CSF), potentially affecting the immature brain of preterm neonates.

Methods: Using preterm pigs as a model for preterm infants, plasma and CSF samples were collected up to 24 h after SE infection and investigated by untargeted mass spectrometry (MS)-based proteomics. Multiple differentially expressed proteins were further studied in vitro.

Results: The clinical signs of sepsis and neuroinflammation in SE-infected piglets were associated with changes of multiple CSF and plasma proteins. Eight plasma proteins, including APOA4, haptoglobin, MBL1, vWF, LBP, and sCD14, were affected 6 h after infection. Acute phase reactants, including complement components, showed a time-dependent activation pattern after infection. Feeding bovine colostrum reduced the sepsis-related changes in clinical indices and plasma proteins. Neuroinflammation-related neuropeptide Y (NPY), IL-18, and MMP-14 showed distinct changes in the CSF and several brain regions (the prefrontal cortex, PVWM, and hippocampus) 24 h after infection. These changes were verified in TLR2 agonist-challenged primary microglia cells, where exogenous NPY suppressed the inflammatory response.

Conclusion: Systemic infection with SE induces inflammation with rapid proteome changes in the plasma and CSF in preterm newborn pigs. The observed early markers of sepsis and neuroinflammation in preterm pigs may serve as novel biomarkers for sepsis in preterm infants.

Factors influencing multinucleated giant cell formation in vitro

Macrophages fuse together to form multinucleated giant cells (MGC) in granulomas associated with various pathological conditions. Improved in vitro methods are required to better enable investigations of MGC biology and potential contribution to disease. There is a need for standardization of MGC quantification, purification of MGC populations, and characterization of how cell culture variables influence MGC formation. This study examined solutions to address these needs while providing context with other current and alternative methods. Primary mouse bone marrow-derived macrophages were treated with interleukin-4, a cytokine known to induce fusion into MGC. This model was used to systematically assess the influence of cell stimulant timing, cell seeding density, colony stimulating factors, and culture vessel type. Results indicated that MGC formation is greatly impacted by alterations in certain culture variables. An assessment of previously published research showed that these culture conditions varied widely between different laboratories, which may explain inconsistencies in the literature. A particularly novel and unexpected observation was that MGC formation appears to be greatly increased by silicone, which is a component of a chamber slide system commonly used for MGC studies. The most successful quantification method was fluorescent staining with semi-automated morphological evaluation. The most successful enrichment method was microfiltration. Overall, this study takes steps toward standardizing in vitro methods, enhancing replicability, and guiding investigators attempting to culture, quantify, and enrich MGC.

Characterization of a functionally active primary microglial cell culture from the pig retina

Retinal inflammation is an integral component of many retinal diseases including diabetic retinopathy (DR), age-related macular degeneration (AMD) and retinopathy of prematurity (ROP). Inflammation is commonly initiated and perpetuated by myeloid-derived immune cells. In the retina, microglial cells are resident macrophages with myeloid origins, which acts as the first responders involved in the innate immune system. To understand the disease pathogenesis, the use of isolated retinal cell culture model is vital for the examination of multiple cellular responses to injury or trauma. The pig retina resembles human retina in terms of tissue architecture, vasculature, and topography. Additionally, it is a better model than the rodent retina because of the presence of the pseudomacula. In the present study, we sought to establish and characterize pig retinal primary microglial cell (pMicroglia) culture. We used pig eyes from the local abattoir and optimized pMicroglia cultures using multiple cell culture conditions and methods. The best results were obtained by seeding cells in DMEM-high glucose media for 18 days followed by shaking of the culture plate. The resulting pMicroglia were characterized by cellular morphology, phenotype, and immunostaining with Iba-1, CD68, P2Y12, CD163, CD14, and Isolectin GS-IB4. Generated pMicroglia were found functionally active in phagocytosis assay and responsive to lipopolysaccharides (LPS) in dose-dependent production of IL-1β. Furthermore, they showed increased secretion of pro-inflammatory cytokines with LPS treatment. Thus, we report a novel and reproducible method for the isolation of primary microglial cells from pig eyes, which may be useful for studying retinal diseases.

Regulation of brain microglia by female gonadal steroids

Microglial cells are the primary mediators of the CNS immune defense system and crucial for shaping inflammatory responses. They represent a highly dynamic cell population which is constantly moving and surveying their environment. Acute brain damage causes a local attraction and activation of this immune cell type which involves neuron-to-glia and glia-to-glia interactions. The prevailing view attributes microglia a "negative" role such as defense and debris elimination. More topical studies also suggest a protective and "positive" regulatory function. Estrogens and progestins exert anti-inflammatory and neuroprotective effects in the CNS in acute and chronic brain diseases. Recent work revealed that microglial cells express subsets of classical and non-classical estrogen and progesterone receptors in a highly dynamic way. In this review article, we would like to stress the importance of microglia for the spreading of neural damage during hypoxia, their susceptibility to functional modulation by sex steroids, the potency of sex hormones to switch microglia from a pro-inflammatory M1 to neuroprotective M2 phenotype, and the regulation of pro- and anti-inflammatory properties including the inflammasome. We will further discuss the possibility that the neuroprotective action of sex steroids in the brain involves an early and direct modulation of local microglia cell function. This article is part of a Special Issue entitled 'Sex steroids and brain disorders'.

Inflammation induces multinucleation of Microglia via PKC inhibition of cytokinesis, generating highly phagocytic multinucleated giant cells

Microglia are brain macrophages, which can undergo multinucleation to give rise to multinucleated giant cells that accumulate with ageing and some brain pathologies. However, the origin, regulation and function of multinucleate microglia remain unclear. We found that inflammatory stimuli, including lipopolysaccharide, amyloid β, α-synuclein, tumour necrosis factor-α and interferon γ, but not interleukin-4, induced multinucleation of cultured microglia: primary rat cortical microglia and the murine microglial cell line BV-2. Inflammation-induced multinucleation was prevented by a protein kinase C (PKC) inhibitor Gö6976 (100 nM) and replicated by a PKC activator phorbol myristate acetate (160 nM). Multinucleation was reversible and not because of cell fusion or phagocytosis, but rather failure of cytokinesis. Time-lapse imaging revealed that some dividing cells failed to abscise, even after formation of long cytoplasmic bridges, followed by retraction of bridge and reversal of cleavage furrow to form multinucleate cells. Multinucleate microglia were larger and 2-4 fold more likely to phagocytose large beads and both dead and live PC12 cells. We conclude that multinucleate microglia are reversibly generated by inflammation via PKC inhibition of cytokinesis, and may have specialized functions/dysfunctions including the phagocytosis of other cells. Inflammation resulted in the accumulation of multiple nuclei per cell in cultured microglia. This multinucleation was reversible and due to a PKC-dependent block of the last step of cell division. Multinucleate microglia were larger and had a greater capacity to phagocytose other cells, suggesting they might remove neurons in the brain.

Osteopontin alters the functional profile of porcine microglia in vitro

OPN (osteopontin) is a secreted glycoprotein predominantly expressed in bone matrix and kidney tissue. More recently, a neuroprotective role has been attributed to this cytokine since it can be up-regulated by microglia in neurodegeneration and inflammation. We demonstrate the expression of OPN within primary cultured microglia. Microglia incubated in vitro with different concentrations (0.1 fM-1 nM) of recombinant OPN showed increased proliferation at 10 fM. Moreover, conditioned medium of LLC-PK1 cells, a pig renal epithelial cell line and a known source of secreted OPN, more than doubled the rate of proliferation of microglia. Addition of an anti-OPN polyclonal antibody completely reversed this effect. Treatment with OPN dose-dependently also inhibited microglial superoxide production. In contrast, phagocytosis of fluorescent-labelled beads was enhanced by OPN. In conclusion, OPN shifts microglia, at least in vitro, to an alternative functional profile more fit to the immune-balanced microenvironment of the CNS (central nervous system).

Microglia activation by SIV-infected macrophages: alterations in morphology and cytokine secretion

HIV infection in the brain and the resultant encephalitis affect approximately one third of individuals infected with HIV, regardless of treatment with antiretroviral drugs. Microglia are the resident phagocytic cell type in the brain, serving as a "first responder" to neuroinvasion by pathogens. The early events of the microglial response to productively infected monocyte/macrophages entering the brain can best be investigated using in vitro techniques. We hypothesized that activation of microglia would be specific to the presence of simian immunodeficiency virus (SIV)-infected macrophages as opposed to responses to macrophages in general. Purified microglia were grown and stimulated with control or SIV-infected macrophages. After 6 h, aliquots of the supernatant were analyzed for 23 cytokines using Millipore nonhuman primate-specific kit. In parallel experiments, morphologic changes and cytokine expression by individual microglia were examined by immunofluorescence. Surprisingly, the presence of macrophages was more important to the microglial response rather than whether the macrophages were infected with SIV. None of the cytokines examined were unique to co-incubation with SIV-infected macrophages compared with control macrophages, or their supernatants. Media from SIV-infected macrophages, however, did induce secretion of higher levels of IL-6 and IL-8 than the other treatments. As resident macrophages in the brain, microglia would be expected to have a strong response to infiltrate innate immune cells such as monocyte/macrophages. This response is triggered by incubation with macrophages, irrespective of whether or not they are infected with SIV, indicating a rapid, generalized immune response when infiltrating macrophages entering the brain.

Granulocyte macrophage colony-stimulating factor enhances the modulatory effect of cytokines on monocyte-derived multinucleated giant cell formation and fungicidal activity against Paracoccidioides brasiliensis

Multinucleated giant cells (MGC) are cells present in characteristic granulomatous inflammation induced by intracellular infectious agents or foreign materials. The present study evaluated the modulatory effect of granulocyte macrophage colony-stimulating factor (GM-CSF) in association with other cytokines such as interferon-gamma (IFN-γ), tumour necrosis factor-alpha, interleukin (IL)-10 or transforming growth factor beta (TGF-β1) on the formation of MGC from human peripheral blood monocytes stimulated with Paracoccidioides brasiliensis antigen (PbAg). The generation of MGC was determined by fusion index (FI) and the fungicidal activity of these cells was evaluated after 4 h of MGC co-cultured with viable yeast cells of P. brasiliensis strain 18 (Pb18). The results showed that monocytes incubated with PbAg and GM-CSF plus IFN-γ had a significantly higher FI than in all the other cultures, while the addition of IL-10 or TGF-β1 had a suppressive effect on MGC generation. Monocytes incubated with both pro and anti-inflammatory cytokines had a higher induction of foreign body-type MGC rather than Langhans-type MGC. MGC stimulated with PbAg and GM-CSF in association with the other cytokines had increased fungicidal activity and the presence of GM-CSF also partially inhibited the suppressive effects of IL-10 and TGF-β1. Together, these results suggest that GM-CSF is a positive modulator of PbAg-stimulated MGC generation and on the fungicidal activity against Pb18.

Cultured adult porcine astrocytes and microglia express functional interferon-γ receptors and exhibit toxicity towards SH-SY5Y cells

In vitro cultures of various glial cell types are common systems used to model neuroinflammatory processes associated with age-dependent human neurodegenerative diseases. Even though most researchers choose to use neonatal rodent brain tissues as the source of glial cells, there are significant variations in glial cell functions that are species and age dependent. It has been established that human and swine immune systems have a number of similarities, which suggests that cultured porcine microglia and astrocytes may be good surrogates for human glial cell types. Here we describe a method that could be used to prepare more than 90% pure microglia and astrocyte cultures derived from adult porcine tissues. We demonstrate that both microglia and astrocytes derived from adult porcine brains express functional interferon-γ receptors (IFN-γ-R) and CD14. They become toxic towards SH-SY5Y neuroblastoma cells when exposed to proinflammatory mediators. Upon such stimulation with lipopolysaccharide (LPS) and interferon-γ (IFN-γ), adult porcine microglia, but not astrocytes, secrete tumor necrosis factor-α (TNF-α) while both cell types do not secrete detectable levels of nitric oxide (NO). Comparison of our experimental data with previously published studies indicates that adult porcine glial cultures have certain functional characteristics that make them similar to human glial cells. Therefore adult porcine glial cells may be a useful model system for studies of human diseases associated with adulthood and advanced age. Adult porcine tissues are relatively easy to obtain in most countries and could be used as a reliable and inexpensive source of cultured cells.

Microglia cell culture: a primer for the novice

Microglial cells are the resident immune cells of the central nervous system. Progress in the recent decade has clearly established that microglial cells participate or even actively drive neurological disease. Much of our current knowledge has been generated by investigating microglial cells in cell culture. The aim of this chapter is to give the uninitiated a basic and adaptable protocol for the culturing of microglial cells. We discuss the challenges of microglial cell culture and provide a collection of tips which reflect our 25+ years of collective experience.

Allogeneic stromal cell implantation in brain tissue leads to robust microglial activation

Although adult and embryonic stem cell-based therapy for central nervous system (CNS) injury is being developed worldwide, less attention is given to the immunological aspects of allogeneic cell implantation in the CNS. The latter is of major importance because, from a practical point of view, future stem cell-based therapy for CNS injury will likely be performed using well-characterised allogeneic stem cell populations. In this study, we aimed to further describe the immunological mechanism leading to rejection of allogeneic bone marrow-derived stromal cells (BM-SC) after implantation in murine CNS. For this, we first investigated the impact of autologous and allogeneic BM-SC on microglia activation in vitro. Although the results indicate that both autologous and allogeneic BM-SC do not activate microglia themselves in vitro, they also do not inhibit activation of microglia after exogenous stimuli in vitro. Next, we investigated the impact of allogeneic BM-SC on microglia activation in vivo. In contrast to the in vitro observations, microglia become highly activated in vivo after implantation of allogeneic BM-SC in the CNS of immune-competent mice. Moreover, our results suggest that microglia, rather than T-cells, are the major contributors to allograft rejection in the CNS.

Effects of the pig renal epithelial cell line LLC-PK1 and its conditioned medium on the phenotype of porcine microglia in vitro

Microglia are dispersed throughout the central nervous system. Under physiological circumstances they display a 'ramified' resting phenotype. In different neuropathologies microglia reversibly transform into the activated form, an amoeboid phagocyte with a broad spectrum of immune effector functions. In this study, a coculture of porcine microglia and the pig renal epithelial cell line LLC-PK1 was used to investigate microglial cell biology. The morphology of the cocultures was elucidated as well as the functionality of the microglia cells by proliferation, superoxide and phagocytosis assays. Our results demonstrate that direct intercellular contact between the two cell types was necessary for microglia to acquire a ramified morphology. Moreover, the conditioned medium of the renal cells promoted proliferation of microglia, inhibited giant cell formation and stimulated microglia to retain their capability to generate superoxide and to perform phagocytosis. In conclusion, we have constructed a cell culture system showing differentiation of microglia in vitro and keeping them in optimal conditions.

Effects of low dose GM-CSF on microglial inflammatory profiles to diverse pathogen-associated molecular patterns (PAMPs)

Background

It is well appreciated that obtaining sufficient numbers of primary microglia for in vitro experiments has always been a challenge for scientists studying the biological properties of these cells. Supplementing culture medium with granulocyte-macrophage colony-stimulating factor (GM-CSF) partially alleviates this problem by increasing microglial yield. However, GM-CSF has also been reported to transition microglia into a dendritic cell (DC)-like phenotype and consequently, affect their immune properties.

Methods

Although the concentration of GM-CSF used in our protocol for mouse microglial expansion (0.5 ng/ml) is at least 10-fold less compared to doses reported to affect microglial maturation and function (≥ 5 ng/ml), in this study we compared the responses of microglia derived from mixed glial cultures propagated in the presence/absence of low dose GM-CSF to establish whether this growth factor significantly altered the immune properties of microglia to diverse bacterial stimuli. These stimuli included the gram-positive pathogen Staphylococcus aureus (S. aureus) and its cell wall product peptidoglycan (PGN), a Toll-like receptor 2 (TLR2) agonist; the TLR3 ligand polyinosine-polycytidylic acid (polyI:C), a synthetic mimic of viral double-stranded RNA; lipopolysaccharide (LPS) a TLR4 agonist; and the TLR9 ligand CpG oligonucleotide (CpG-ODN), a synthetic form of bacteria/viral DNA.

Results

Interestingly, the relative numbers of microglia recovered from mixed glial cultures following the initial harvest were not influenced by GM-CSF. However, following the second and third collections of the same mixed cultures, the yield of microglia from GM-CSF-supplemented flasks was increased two-fold. Despite the ability of GM-CSF to expand microglial numbers, cells propagated in the presence/absence of GM-CSF demonstrated roughly equivalent responses following S. aureus and PGN stimulation. Specifically, the induction of tumor necrosis factor-α (TNF-α), macrophage inflammatory protein-2 (MIP-2/CXCL2), and major histocompatibility complex (MHC) class II, CD80, CD86 expression by microglia in response to S. aureus were similar regardless of whether cells had been exposed to GM-CSF during the mixed culture period. In addition, microglial phagocytosis of intact bacteria was unaffected by GM-CSF. In contrast, upon S. aureus stimulation, CD40 expression was induced more prominently in microglia expanded in GM-CSF. Analysis of microglial responses to additional pathogen-associate molecular patterns (PAMPs) revealed that low dose GM-CSF did not significantly alter TNF-α or MIP-2 production in response to the TLR3 and TLR4 agonists polyI:C or LPS, respectively; however, cells expanded in the presence of GM-CSF produced lower levels of both mediators following CpG-ODN stimulation.

Conclusion

We demonstrate that low levels of GM-CSF are sufficient to expand microglial numbers without significantly affecting their immunological responses following activation of TLR2, TLR4 or TLR3 signaling. Therefore, low dose GM-CSF can be considered as a reliable method to achieve higher microglial yields without introducing dramatic activation artifacts.

Formation of multinucleated giant cells and microglial degeneration in rats expressing a mutant Cu/Zn superoxide dismutase gene

BACKGROUND

Microglial neuroinflammation is thought to play a role in the pathogenesis of amyotrophic lateral sclerosis (ALS). The purpose of this study was to provide a histopathological evaluation of the microglial neuroinflammatory response in a rodent model of ALS, the SOD1G93A transgenic rat.

METHODS

Multiple levels of the CNS from spinal cord to cerebral cortex were studied in SOD1G93A transgenic rats during three stages of natural disease progression, including presymptomatic, early symptomatic (onset), and late symptomatic (end stage), using immuno- and lectin histochemical markers for microglia, such as OX-42, OX-6, and Griffonia simplicifolia isolectin B4.

RESULTS

Our studies revealed abnormal aggregates of microglia forming in the spinal cord as early as the presymptomatic stage. During the symptomatic stages there was prominent formation of multinucleated giant cells through fusion of microglial cells in the spinal cord, brainstem, and red nucleus of the midbrain. Other brain regions, including substantia nigra, cranial nerve nuclei, hippocampus and cortex showed normal appearing microglia. In animals during end stage disease at 4-5 months of age virtually all microglia in the spinal cord gray matter showed extensive fragmentation of their cytoplasm (cytorrhexis), indicative of widespread microglial degeneration. Few microglia exhibiting nuclear fragmentation (karyorrhexis) indicative of apoptosis were identified at any stage.

CONCLUSION

The current findings demonstrate the occurrence of severe abnormalities in microglia, such as cell fusions and cytorrhexis, which may be the result of expression of mutant SOD1 in these cells. The microglial changes observed are different from those that accompany normal microglial activation, and they demonstrate that aberrant activation and degeneration of microglia is part of the pathogenesis of motor neuron disease.

Advances in swine biomedical model genomics

This review is a short update on the diversity of swine biomedical models and the importance of genomics in their continued development. The swine has been used as a major mammalian model for human studies because of the similarity in size and physiology, and in organ development and disease progression. The pig model allows for deliberately timed studies, imaging of internal vessels and organs using standard human technologies, and collection of repeated peripheral samples and, at kill, detailed mucosal tissues. The ability to use pigs from the same litter, or cloned or transgenic pigs, facilitates comparative analyses and genetic mapping. The availability of numerous well defined cell lines, representing a broad range of tissues, further facilitates testing of gene expression, drug susceptibility, etc. Thus the pig is an excellent biomedical model for humans. For genomic applications it is an asset that the pig genome has high sequence and chromosome structure homology with humans. With the swine genome sequence now well advanced there are improving genetic and proteomic tools for these comparative analyses. The review will discuss some of the genomic approaches used to probe these models. The review will highlight genomic studies of melanoma and of infectious disease resistance, discussing issues to consider in designing such studies. It will end with a short discussion of the potential for genomic approaches to develop new alternatives for control of the most economically important disease of pigs, porcine reproductive and respiratory syndrome (PRRS), and the potential for applying knowledge gained with this virus for human viral infectious disease studies.