Monkeypox infection: The past, present, and future

Monkeypox is a zoonotic illness caused by the monkeypox virus (MPXV) that has a similar etiology to smallpox. The first case of monkeypox was reported in Western and Central Africa in 1971, and in 2003, there was an outbreak of monkeypox viruses outside Africa. According to the World Health Organization (WHO) and Center for Disease Control and Prevention (CDC), monkeypox is transmitted through direct contact with infected animals or persons exposed to infectious sores, scabs, or body fluids. Also, intimate contact between people during sex, kissing, cuddling, or touching parts of the body can result in the spreading of this disease. The use of the smallpox vaccine against monkeypox has several challenges and hence anti-virals such as cidofovir, brincidofovir, and tecovirimat have been used for the symptomatic relief of patients and reversing the lesion formation on the skin. Despite the recent outbreak of monkeypox most especially in hitherto non-endemic countries, there is still a lack of definitive treatment for monkeypox. In the present review, emphasis was focused on etiopathology, transmission, currently available therapeutic agents, and future targets that could be explored to halt the progression of monkeypox. From our review we can postulate that owing to the lack of a definitive cure to this reemerging disorder, there is a need for general awareness about the transmission as well as to develop appropriate diagnostic procedures, immunizations, and antiviral medication.

Messenger ribonucleic acid vaccines for severe acute respiratory syndrome coronavirus-2 - a review

The mRNA therapeutics have been studied since the 1970s and the currently available mRNA vaccines against COVID-19 are the culmination of decades of scientific research. The mRNA vaccines BNT162b2 and mRNA-1273 have played a key role in our global response to the COVID-19 pandemic as they have demonstrated significant advantages over conventional vaccines and have proven to be highly effective against COVID-19 associated hospitalization and severe illness in large clinical trials and studies using real-world data.

Notch-Mediated Generation of Monocyte-Derived Langerhans Cells: Phenotype and Function

Langerhans cells (LCs) in the skin are a first line of defense against pathogens but also play an essential role in skin homeostasis. Their exclusive expression of the C-type lectin receptor Langerin makes them prominent candidates for immunotherapy. For vaccine testing, an easily accessible cell platform would be desirable as an alternative to the time-consuming purification of LCs from human skin. Here, we present such a model and demonstrate that monocytes in the presence of GM-CSF, TGF-β1, and the Notch ligand DLL4 differentiate within 3 days into CD1a+Langerin+cells containing Birbeck granules. RNA sequencing of these monocyte-derived LCs (moLCs) confirmed gene expression of LC-related molecules, pattern recognition receptors, and enhanced expression of genes involved in the antigen-presenting machinery. On the protein level, moLCs showed low expression of costimulatory molecules but prominent expression of C-type lectin receptors. MoLCs can be matured, secrete IL-12p70 and TNF-α, and stimulate proliferation and cytokine production in allogeneic CD4+ and CD8+ T cells. In regard to vaccine testing, a recently characterized glycomimetic Langerin ligand conjugated to liposomes demonstrated specific and fast internalization into moLCs. Hence, these short-term in vitro‒generated moLCs represent an interesting tool to screen LC-based vaccines in the future.

Lack of Type 2 Innate Lymphoid Cells Promotes a Type I-Driven Enhanced Immune Response in Contact Hypersensitivity

Allergic contact dermatitis and its animal model, contact hypersensitivity, are T-cell-mediated inflammatory skin diseases that require activation of the innate immune system. Here we investigate the role of innate lymphoid cells (ILCs) during the elicitation phase of 2,4,6-trinitrochlorobenzene-induced contact hypersensitivity using EomesGfp/+ x Rorc(γt)-CreTg x Rosa26RYfp/+ reporter mice. Ear swelling responses, cutaneous ILC numbers, and cytokine production were determined at different time points. Functional analyses were performed in a CD90.1/.2 congenic adoptive transfer model that allowed selective antibody-mediated depletion of ILCs before hapten challenge, and in Rorasg/floxIl7rCre/+ mice, which lack ILC2. Hapten challenge induced early increases of natural killer cells in skin and ear draining lymph nodes corresponding to the peak ear swelling response. In contrast, ILC1, 2, and 3 showed a delayed increase in numbers corresponding to the contact hypersensitivity resolution phase. Hapten challenge induced increased marker cytokines in all ILC subtypes and an activated phenotype in ILC2. Depletion of all ILC resulted in a significantly enhanced ear swelling response. Similarly, ILC2-deficient mice (Rorasg/floxIl7rCre/+) displayed increased ear swelling responses on hapten challenge, suggesting that ILC2 act as negative regulators in the type 1-dominated immune response of contact hypersensitivity.

Oncogene-Expressing Senescent Melanocytes Up-Regulate MHC Class II, a Candidate Melanoma Suppressor Function

On acquisition of an oncogenic mutation, primary human and mouse cells can enter oncogene-induced senescence (OIS). OIS is characterized by a stable proliferation arrest and secretion of proinflammatory cytokines and chemokines, the senescence-associated secretory phenotype. Proliferation arrest and the senescence-associated secretory phenotype collaborate to enact tumor suppression, the former by blocking cell proliferation and the latter by recruiting immune cells to clear damaged cells. However, the interactions of OIS cells with the immune system are still poorly defined. Here, we show that engagement of OIS in primary human melanocytes, specifically by melanoma driver mutations NRASQ61K and BRAFV600E, causes expression of the major histocompatibility class II antigen presentation apparatus, via secreted IL-1ß signaling and expression of CIITA, a master regulator of major histocompatibility class II gene transcription. In vitro, OIS melanocytes activate T-cell proliferation. In vivo, nonproliferating oncogene-expressing melanocytes localize to skin-draining lymph nodes, where they induce T-cell proliferation and an antigen presentation gene expression signature. In patients, expression of major histocompatibility class II in melanoma is linked to favorable disease outcome. We propose that OIS in melanocytes is accompanied by an antigen presentation phenotype, likely to promote tumor suppression via activation of the adaptive immune system.

Neuroimmunological processes in Parkinson's disease and their relation to α-synuclein: microglia as the referee between neuronal processes and peripheral immunity

The role of neuroinflammation and the adaptive immune system in PD (Parkinson's disease) has been the subject of intense investigation in recent years, both in animal models of parkinsonism and in post-mortem PD brains. However, how these processes relate to and modulate α-syn (α-synuclein) pathology and microglia activation is still poorly understood. Specifically, how the peripheral immune system interacts, regulates and/or is induced by neuroinflammatory processes taking place during PD is still undetermined. We present herein a comprehensive review of the features and impact that neuroinflamation has on neurodegeneration in different animal models of nigral cell death, how this neuroinflammation relates to microglia activation and the way microglia respond to α-syn in vivo. We also discuss a possible role for the peripheral immune system in animal models of parkinsonism, how these findings relate to the state of microglia activation observed in these animal models and how these findings compare with what has been observed in humans with PD. Together, the available data points to the need for development of dual therapeutic strategies that modulate microglia activation to change not only the way microglia interact with the peripheral immune system, but also to modulate the manner in which microglia respond to encounters with α-syn. Lastly, we discuss the immune-modulatory strategies currently under investigation in animal models of parkinsonism and the degree to which one might expect their outcomes to translate faithfully to a clinical setting.

Association of the chicken MHC B haplotypes with resistance to avian coronavirus

Clinical respiratory illness was compared in five homozygous chicken lines, originating from homozygous B2, B8, B12 and B19, and heterozygous B2/B12 birds after infection with either of two strains of the infectious bronchitis virus (IBV). All chickens used in these studies originated from White Leghorn and Ancona linages. IBV Gray strain infection of MHC homozygous B12 and B19 haplotype chicks resulted in severe respiratory disease compared to chicks with B2/B2 and B5/B5 haplotypes. Demonstrating a dominant B2 phenotype, B2/B12 birds were also more resistant to IBV. Respiratory clinical illness in B8/B8 chicks was severe early after infection, while illness resolved similar to the B5 and B2 homozygous birds. Following M41 strain infection, birds with B2/B2 and B8/B8 haplotypes were again more resistant to clinical illness than B19/B19 birds. Real time RT-PCR indicated that infection was cleared more efficiently in trachea, lungs and kidneys of B2/B2 and B8/B8 birds compared with B19/B19 birds. Furthermore, M41 infected B2/B2 and B8/B8 chicks performed better in terms of body weight gain than B19/B19 chicks. These studies suggest that genetics of B defined haplotypes might be exploited to produce chicks resistant to respiratory pathogens or with more effective immune responses.

Viral models of multiple sclerosis: neurodegeneration and demyelination in mice infected with Theiler's virus

Multiple sclerosis (MS) is a complex inflammatory disease of unknown etiology that affects the central nervous system (CNS) white matter, and for which no effective cure exists. Indeed, whether the primary event in MS pathology affects myelin or axons of the CNS remains unclear. Animal models are necessary to identify the immunopathological mechanisms involved in MS and to develop novel therapeutic and reparative approaches. Specifically, viral models of chronic demyelination and axonal damage have been used to study the contribution of viruses in human MS, and they have led to important breakthroughs in our understanding of MS pathology. The Theiler's murine encephalomyelitis virus (TMEV) model is one of the most commonly used MS models, although other viral models are also used, including neurotropic strains of mouse hepatitis virus (MHV) that induce chronic inflammatory demyelination with similar histological features to those observed in MS. This review will discuss the immunopathological mechanisms involved in TMEV-induced demyelinating disease (TMEV-IDD). The TMEV model reproduces a chronic progressive disease due to the persistence of the virus for the entire lifespan in susceptible mice. The evolution and significance of the axonal damage and neuroinflammation, the importance of epitope spread from viral to myelin epitopes, the presence of abortive remyelination and the existence of a brain pathology in addition to the classical spinal cord demyelination, are some of the findings that will be discussed in the context of this TMEV-IDD model. Despite their limitations, viral models remain an important tool to study the etiology of MS, and to understand the clinical and pathological variability associated with this disease.

Weak binder for MHC molecule is a potent Mycobacterium tuberculosis-specific CTL epitope in the context of HLA-A24 allele

Tuberculosis causes serious health problem for the world population. Antigenic peptides selected by pathogen-specific cytotoxic T lymphocytes (CTLs) are presented by major histocompatibility complex (MHC; or human leukocyte antigen [HLA] in humans) molecules, and HLA-A restricted responses may be of interest for vaccine development and the understanding of cellular immunity. A series of peptides derived from the 10-KDa culture filtrate protein (CFP10) and the 6 kDa early secretory antigenic target (ESAT-6) in the Mycobacterium tuberculosis (Mtb) have been screened and a CTL epitope restricted by the human leukocyte antigen HLA-A24, a common HLA allele in Asian people, has been identified. In this study, we studied a panel of CFP10 and ESAT-6-derived peptides to identify those with binding motifs for HLA-A24 molecules. The antigenicity of candidate peptides was assessed with in vitro refolding tests and an enzyme-linked immunospot (ELISPOT) assay, and by tetramer staining to determine the capacity to stimulate CTLs from peripheral blood mononuclear cells (PBMCs) of HLA-A24-positive TB Patients. We report that one novel candidate peptide at positions 5-14 of ESAT-6 of Mtb could induce peptide-specific CTLs from PBMCs of HLA-A24-positive patients, but not from HLA-A24-negative patients and HLA-A24-positive healthy controls. Identified epitope is a weak binder for HLA-A24 molecule in a mini MHC refolding assay. Since the peptide is presented by a common HLA class I molecule, it may be useful for immunotherapy against Mtb infection and vaccine development in the large population of Mtb-infected patients.

Stem cells and cell therapy approaches in lung biology and diseases

Cell-based therapies with embryonic or adult stem cells, including induced pluripotent stem cells, have emerged as potential novel approaches for several devastating and otherwise incurable lung diseases, including emphysema, pulmonary fibrosis, pulmonary hypertension, and the acute respiratory distress syndrome. Although initial studies suggested engraftment of exogenously administered stem cells in lung, this is now generally felt to be a rare occurrence of uncertain physiologic significance. However, more recent studies have demonstrated paracrine effects of administered cells, including stimulation of angiogenesis and modulation of local inflammatory and immune responses in mouse lung disease models. Based on these studies and on safety and initial efficacy data from trials of adult stem cells in other diseases, groundbreaking clinical trials of cell-based therapy have been initiated for pulmonary hypertension and for chronic obstructive pulmonary disease. In parallel, the identity and role of endogenous lung progenitor cells in development and in repair from injury and potential contribution as lung cancer stem cells continue to be elucidated. Most recently, novel bioengineering approaches have been applied to develop functional lung tissue ex vivo. Advances in each of these areas will be described in this review with particular reference to animal models.

Immunology of the Testis and Male Reproductive Tract

A large body of evidence points to the existence of a close, dynamic relationship between the immune system and the male reproductive tract, which has important implications for our understanding of both systems. The testis and the male reproductive tract provide an environment that protects the otherwise highly immunogenic spermatogenic cells and sperm from immunological attack. At the same time, secretions of the testis, including androgens, influence the development and mature functions of the immune system. Activation of the immune system has negative effects on both androgen and sperm production, so that systemic or local infection and inflammation compromise male fertility. The mechanisms underlying these interactions have begun to receive the attention from reproductive biologists and immunologists that they deserve, but many crucial details remain to be uncovered. A complete picture of male reproductive tract function and its response to toxic agents is contingent upon continued exploration of these interactions and the mechanisms involved.

Rabies DNA vaccine: no impact of MHC class I and class II targeting sequences on immune response and protection against lethal challenge

Rabies is progressive fatal encephalitis. WHO estimates 55,000 rabies deaths and more than 10 million PEP every year world-wide. A variety of cell-culture derived vaccines are available for prophylaxis against rabies. However, their high cost restricts their usage in developing countries, where such cases are most often encountered. This is driving the quest for newer vaccine formulations; DNA vaccines being most promising amongst them. Here, we explored strategies of antigen trafficking to various cellular compartments aiming at improving both humoral and cellular immunity. These strategies include use of signal sequences namely Tissue Plasminogen Activator (TPA), Ubiquitin (UQ) and Lysosomal-Associated Membrane Protein-1 (LAMP-1). TPA, LAMP-1 and their combination were aimed at enhancing the CD4(+) T cell and antibody response. In contrast, the UQ tag was utilized for enhancing CD8(+) response. The potency of modified DNA vaccines assessed by total antibody response, antibody isotypes, cytokine profile, neutralizing antibody titer and protection conferred against in vivo challenge; was enhanced in comparison to native unmodified vaccine, but the response elicited did not pertain to the type of target sequence and the directed arm of immunity. Interestingly, the DNA vaccines that had been designed to generate different type of immune responses yielded in effect similar response. In conclusion, our data indicate that the directing target sequence is not the exclusive deciding factor for type and extent of immune response elicited and emphasizes on the antigen dependence of immune enhancement strategies.

Minute virus of mice: antibody response, viral shedding, and persistence of viral DNA in multiple strains of mice

Minute virus of mice (MVM) is a major concern for laboratory animal facilities because it remains with considerably high prevalence despite strict barrier systems. The aim of this study was to elucidate potential risks associated with MVM infection by investigating the role of the genetic background on antibody production and persistence as well as viral shedding. Mice of various strains and stocks were inoculated oronasally with the immunosuppressive strain MVMi; in addition, natural infection was modeled through contact exposure. As determined by serology, seroconversion and serum levels of IgG differed considerably among strains and stocks, especially in the contact-exposed group. For example, C57BL/6J mice responded well to exposure in contrast to FVB/N, NMRI, ICR, and C3H/HeN mice. Titration studies indicated that the viral dose necessary to induce seroconversion was strain-dependent. Experiments to dissect the role of the major histocompatibility complex haplotype in the response to MVMi gave inconclusive results. To detect viral persistence, spleens and feces were analyzed by PCR at 16 wk after exposure, and the infectivity of PCR-positive spleens was investigated by IP and oronasal inoculation of naive mice. Although DNA was detected in the spleens of some mice, feces remained negative, and naive mice were not infected by inoculation. In addition, viral shedding declined rapidly after day 20 postinoculation. In summary, the data show that seroconversion and antibody response to MVMi infection depend on the genetic background of mice, with the infective dose being a critical factor. The role of viral DNA in chronically infected mice will require further elucidation.

The guinea pig as a model of infectious diseases

The words 'guinea pig' are synonymous with scientific experimentation, but much less is known about this species than many other laboratory animals. This animal model has been used for approximately 200 y and was the first to be used in the study of infectious diseases such as tuberculosis and diphtheria. Today the guinea pig is used as a model for a number of infectious bacterial diseases, including pulmonary, sexually transmitted, ocular and aural, gastrointestinal, and other infections that threaten the lives of humans. Most studies on the immune response to these diseases, with potential therapies and vaccines, have been conducted in animal models (for example, mouse) that may have less similarity to humans because of the large number of immunologic reagents available for these other species. This review presents some of the diseases for which the guinea pig is regarded as the premier model to study infections because of its similarity to humans with regard to symptoms and immune response. Furthermore, for diseases in which guinea pigs share parallel pathogenesis of disease with humans, they are potentially the best animal model for designing treatments and vaccines. Future studies of immune regulation of these diseases, novel therapies, and preventative measures require the development of new immunologic reagents designed specifically for the guinea pig.

Combinational clustering of receptors following stimulation by bacterial products determines lipopolysaccharide responses

The innate immune system has the capacity to recognize a wide range of pathogens based on conserved PAMPs (pathogen-associated molecular patterns). In the case of bacterial LPS (lipopolysaccharide) recognition, the best studied PAMP, it has been shown that the innate immune system employs at least three cell-surface receptors: CD14, TLR4 (Toll-like receptor 4) and MD-2 protein. CD14 binds LPS from Enterobacteriaceae and then transfers it to MD-2, leading to TLR4 aggregation and signal transduction. LPS analogues such as lipid IVa seem to act as LPS antagonists in human cells, but exhibit LPS mimetic activity in mouse cells. Although TLR4 has been shown to be involved in this species-specific discrimination, the mechanism by which this is achieved has not been elucidated. The questions that remain are how the innate immune system can discriminate between LPS from different bacteria as well as different LPS analogues, and whether or not the structure of LPS affects its interaction with the CD14-TLR4-MD-2 cluster. Is it possible that the 'shape' of LPS induces the formation of different receptor clusters, and thus a different immune response? In the present study, we demonstrate using biochemical as well as fluorescence-imaging techniques that different LPS analogues trigger the recruitment of different receptors within microdomains. The composition of each receptor cluster as well as the number of TLR4 molecules that are recruited within the cluster seem to determine whether an immune response will be induced or inhibited.

The major histocompatibility complex influences the ethiopathogenesis of MS-like disease in primates at multiple levels

Multiple sclerosis (MS) is a chronic inflammatory demyelinating disease primarily affecting the central nervous system. Of the many candidate polymorphic major histocompatibility complex (MHC) and non-MHC genes contributing to disease susceptibility, including those encoding effector (cytokines and chemokines) or receptor molecules within the immune system (MHC, TCR, Ig or FcR), human leukocyte antigen (HLA) class II genes have the most significant influence. In this article we put forward the hypothesis that the influence of HLA genes on the risk to develop MS is actually the sum of multiple antigen presenting cell (APC) and T-cell interactions involving HLA class I and class II molecules. This article will also discuss that, because of the genetic and immunologic similarity to humans, autoimmune models of MS in non-human primates are the experimental models "par excellence" to test this hypothesis.

An unique CD4+CD8+ intestinal intraepithelial lymphocyte specific for DnaK (Escherichia coli HSP70) may be selected by intestinal microflora of rats

We have previously shown an age-associated increase in unique CD4+CD8+ intestinal intraepithelial lymphocytes (i-IEL) in rats. To elucidate the potential causes of the increase in CD4+CD8+ i-IEL with age, we analyzed the specificity of the CD4+CD8+ i-IEL and influence of intestinal microflora on the increase in this subset in aged rats. The purified CD4+CD8+ i-IEL proliferated in response to DnaK [Escherichia coli (E. coli) HSP70] in the presence of mitomycin-c (MMC)-treated syngeneic spleen cells. The proportion of CD4+CD8+ T cells in whole i-IEL were significantly increased in aged rats fed commercial (CL-2) diet but not in those fed home-made (purified) diet under conventional condition. No CD4+CD8+ i-IEL were detected in aged rats under germfree condition, irrespective of diet feeding. A larger number of Enterobacteriaceae, especially E. coli, were detected in the intestinal contents and feces from aged rats with CD4+CD8+ i-IEL compared with those from aged rats fed without CD4+CD8+ i-IEL. The unique CD4+CD8+ i-IEL population specific for E. coli HSP may be associated with long term exposure to intestinal E. coli in aged rats.

Cytokine network in the central nervous system and its roles in growth and differentiation of glial and neuronal cells

Cells resident within the central nervous system (CNS) can synthesize, secrete and respond to inflammatory cytokines not only contributing to the responses to injury or immunological challenge within the CNS, but also regulating their own growth and differentiation potential. The actions and cell communication via cytokines in the CNS are designated as the CNS cytokine network, in which microglia and astrocytes play the central roles. To further characterize the CNS cytokine network we investigated the differences in roles of these cells, and found that microglia might contribute to the early phase of cytokine production reaction and that astrocytes might contribute the late phase of the reaction. We also investigated roles of inhibitory cytokines such as TGF beta, IL-4, and IL-10, and showed that each might play a distinct role in the inhibitory regulation in the CNS. We summarized our previous report about cellular distribution of cytokine receptors in the CNS cells and discussed their roles in the CNS cytokine network. Finally, we investigated that expression of IL-6 and IL-2 receptors in neuronal and oligodendrocytic differentiation, respectively. From these results, we discussed the features of the CNS cytokine network.

Human natural interferon-alpha producing cells

Interferons (IFNs) are critical components of the host immune system, serving as antiviral agents, immunomodulators and inhibitors of cell growth. Among peripheral blood mononuclear cells, the primary IFN-alpha-producing cell is a light density, HLA-DR+ cell negative for cell surface markers typical for T cells, B cells, monocytes, natural-killer or progenitor cells and has been tentatively termed the 'natural IFN-producing cell' or NIPC. Although present in very low frequency (approximately 1:1000 among peripheral blood mononuclear cells), the NIPC are very potent, with an individual cell able to produce 1-2 IU of IFN. In this review, the characteristics, phenotype, regulation and relationship of NIPC to human disease are discussed.

A transient transfection system for identifying biosynthesized proteins processed and presented to class I MHC restricted T lymphocytes

CD8+ cytotoxic T lymphocytes (CTL) constitute a major portion of immune responses to foreign and self antigens. CTL recognize class I major histocompatibility complex molecules complexed to peptides of 8-10 residues derived from cytosolic proteins. To understand CTL responses to these antigens and to manipulate CTL responses optimally, it is necessary to identify the specific peptides recognized by CTL. The methods currently used for this purpose have significant drawbacks. We describe a plasmid transfection method that results in significant lysis of histocompatible target cells. Influenza virus-specific CTLs specifically lysed target cells that were transfected with plasmids bearing cDNAs encoding full length gene products, fragments containing the region that encodes the CTL epitope, or even a ten residue peptide. This significantly lessens the time and effort required to define genes, and gene segments that contain CTL epitopes.

Swine leukocyte antigen and macrophage marker expression on both African swine fever virus-infected and non-infected primary porcine macrophage cultures

Swine leukocyte antigens (SLA) and a macrophage specific marker were monitored on porcine macrophages cultured with or without macrophage colony stimulatory factor (M-CSF) and on cells infected with African swine fever virus (ASFV). SLA expression was maximal either in the total cell extract or on the cell surface at 3-4 days of culture; after 4 days these values began to decrease. Fluorescence analyses of immunostained macrophages cultured with or without M-CSF indicated a major upward shift in the number of SLA Class I molecules on individual macrophages whereas for SLA Class II both a novel expression of Class II and an upward shift in the number of molecules per cell were evident. Infection of 3-day-old macrophage cultures with three different isolates of ASFV resulted in minor changes in surface expression of SLA Class I, SLA Class II, and macrophage markers. No differences in infection with ASFV was observed whether macrophages were SLA Class II positive or negative, nor was there blocking by anti-SLA Class I or Class II monoclonal antibodies of ASFV infection of cultured macrophages.

In vitro mitogen responses and lymphocyte subpopulations in cheetahs

Lack of genetic variability and apparent susceptibility of cheetahs (Acinonyx jubatus jubatus) to coronavirus infection has lead to speculation that this species may have immune system deficits. To establish a foundation for evaluation of the immune function, cheetah peripheral blood mononuclear cells (PBM) were stimulated by a panel of six mitogens, and responses compared with those of domestic cat PBM. Individual responses in both species were variable, but evenly distributed throughout the range of stimulation for each mitogen. Proliferation by PBM from domestic cats occurred within the same range as that of the cheetahs. However, a significantly lower response to peanut agglutinin (PNA) was observed with domestic cat PBM. Although responses varied between animals, certain individual cheetahs were consistent low responders. The decreased values could not be explained by lack of IL-2 responsiveness since exogenous IL-2 significantly enhanced mitogen-stimulated proliferation in 11 of 12 cheetahs tested. The phenotypic distribution of domestic cat and cheetah lymphocyte subpopulations was similar as assessed by immunofluorescence staining for surface immunoglobulin (sIg) and cytotoxic T (Tc) cells (using a specific monoclonal antibody, FT2). Values for B cells (31.2% sIg+) and Tc (28.7% FT2+) were slightly higher in domestic cats as compared with cheetah PBM (13.3% sIg+; 19.0% FT2+). Even though no species-specific deficits were detected, a significant negative correlation between PHA-stimulated proliferation and percent FT2+ (Tc) cheetah cells was observed. This indicates that proliferation can be used indirectly to assess relative numbers of functional T helper cells in cheetahs. Our studies suggest that these aspects of the cheetah's immune system are comparable with the domestic cat, and establish a basis for in vitro assays evaluating antigen-specific responses.

Induction and regulation of class II major histocompatibility complex mRNA expression in astrocytes by interferon-gamma and tumor necrosis factor-alpha

Astrocytes can function as antigen-presenting cells (APC) upon expression of class II major histocompatibility complex (MHC) antigens, which are induced by interferon-gamma (IFN-gamma). Previous data from this laboratory had shown that the cytokine tumor necrosis factor-alpha (TNF-alpha) enhances IFN-gamma-mediated class II antigen expression on astrocytes. We have now investigated the effect of IFN-gamma and TNF-alpha on class II MHC mRNA expression in astrocytes using Northern blot analysis. Astrocytes do not constitutively express mRNA for class II MHC. Kinetic analysis of class II MHC mRNA expression in IFN-gamma-treated cells demonstrated an 8 h time lag, which was followed by an increase over the next 16 h. Optimal expression of class II mRNA was detected after a 24 h incubation with IFN-gamma. This level of expression was further enhanced by the simultaneous addition of IFN-gamma and TNF-alpha to the astrocytes, while TNF-alpha alone had no effect on class II mRNA expression. TNF-alpha does not act by increasing the stability of IFN-gamma-induced class II mRNA, indicating its action is not at that specific level of post-transcriptional control. Furthermore, astrocyte class II mRNA expression was inhibited when cycloheximide (CHX) was added together with IFN-gamma or IFN-gamma/TNF-alpha, and when CHX was added up to 4 h after treatment with IFN-gamma or IFN-gamma/TNF-alpha. These results indicate that astrocyte class II mRNA expression is mediated by newly synthesized proteins induced by IFN-gamma and/or IFN-gamma/TNF-alpha. The expression of class II antigens on astrocytes, and cytokine modulation of their expression, may be important in the initiation and perpetuation of intracerebral immune responses.

Class II-restricted T cell responses in Theiler's murine encephalomyelitis virus (TMEV)-induced demyelinating disease. III. Failure of neuroantigen-specific immune tolerance to affect the clinical course of demyelination

Intracerebral inoculation of Theiler's murine encephalomyelitis virus (TMEV) into susceptible mouse strains produces a chronic demyelinating disease in which mononuclear cell-rich infiltrates in the central nervous system (CNS) are prominent. Current evidence strongly supports an immune-mediated basis for myelin breakdown, with an effector role proposed for TMEV-specific, major histocompatibility complex (MHC) class II-restricted delayed-type hypersensitivity (DTH) responses in which lymphokine-activated macrophages mediate bystander demyelination. The present study examined the possibility that concomitant or later-appearing neuroantigen-specific autoimmune T cell responses, such as those demonstrated in chronic-relapsing experimental allergic encephalomyelitis (R-EAE), may contribute to the demyelinating process following TMEV infection. T cell responses against intact, purified major myelin proteins (myelin basic protein (MBP) and proteolipid protein (PLP], and against altered myelin constituents were readily demonstrable in SJL/J mice with R-EAE, but were not detectable in SJL/J mice with TMEV-induced demyelinating disease. TMEV-infected mice also did not display T cell responses against the peptide fragments of MBP(91-104) and PLP(139-151) recently shown to be encephalitogenic in SJL/J mice. In addition, induction of neuroantigen-specific tolerance to a heterogeneous mixture of CNS antigens, via the i.v. injection of syngeneic SJL/J splenocytes covalently coupled with mouse spinal cord homogenate, resulted in significant suppression of clinical and histologic signs of R-EAE and the accompanying MBP- and PLP-specific DTH responses. In contrast, neuroantigen-specific tolerance failed to alter the development of clinical and histologic signs of TMEV-induced demyelinating disease or the accompanying virus-specific DTH and humoral immune responses. These findings demonstrate that TMEV-induced demyelinating disease can occur in the apparent absence of neuroantigen-specific autoimmune responses. The relationship of the present results to the immunopathology of multiple sclerosis is discussed.

Tumor necrosis factor-alpha enhances interferon-gamma-mediated class II antigen expression on astrocytes

Astrocytes can function as antigen-presenting cells (APC) upon expression of class II antigens, which are induced by interferon-gamma (IFN-gamma). Tumor necrosis factor-alpha (TNF-alpha) can act synergistically with IFN-gamma with respect to class II expression on a variety of cells. As brain cells themselves can secrete TNF-like factors upon stimulation, we examined the effect of TNF-alpha on IFN-gamma-mediated class II induction on astrocytes. TNF-alpha alone had no effect on class II expression, but did synergize with IFN-gamma for enhanced expression of class II antigens. The specificity of TNF-alpha activity was demonstrated by blocking the amplifying effect of TNF-alpha with a polyclonal anti-TNF-alpha antibody. Kinetic analysis of the synergistic effect indicated that optimal TNF-alpha enhancement of class II expression was observed when astrocytes were pretreated with IFN-gamma 12-24 h prior to TNF-alpha addition. A possible mechanism for the synergistic action between IFN-gamma and TNF-alpha may be increased TNF-alpha receptor expression by IFN-gamma. Astrocytes treated with IFN-gamma for 24 h express more TNF-alpha receptors (3900/cell) than do untreated astrocytes (2483/cell), with no significant change in the binding affinity (Kd). These results suggest that the synergistic activity of TNF-alpha requires an inductive signal from IFN-gamma, which in part may be increased TNF-alpha receptor expression. Altogether, our observations indicate that TNF-alpha enhances ongoing class II major histocompatibility complex gene expression in rat astrocytes, which in this system is initially induced by IFN-gamma. TNF-alpha exerts its effect by binding to high affinity TNF-alpha receptors on astrocytes, whose expression is also enhanced by IFN-gamma. These two cytokines work in concert to elevate class II expression on astrocytes, an event which can contribute to initiation and/or perpetuation of intracerebral immune responses.