CD4+ and CD8+ T Cells Make Discrete Contributions to Demyelination and Neurologic Disease in a Viral Model of Multiple Sclerosis

Following intracerebral infection with Theiler’s murine encephalomyelitis virus (TMEV), susceptible strains of mice (SJL and PLJ) develop virus persistence and demyelination similar to that found in human multiple sclerosis. Resistant strains of mice (C57BL/6) clear virus and do not develop demyelination. To resolve the controversy about the role of CD4⁺ and CD8⁺ T cells in the development of demyelination and neurologic deficits in diseases of the central nervous system, we analyzed TMEV infection in CD4- and CD8-deficient B6, PLJ, and SJL mice. Genetic deletion of either CD4 or CD8 from resistant B6 mice resulted in viral persistence and demyelination during the chronic stage of disease. Viral persistence and demyelination were detected in all strains of susceptible background. Although genetic deletion of CD8 had no effect on the extent of demyelination in susceptible strains, deletion of CD4 dramatically increased the degree of demyelination observed. Whereas strains with deletions of CD4 showed severe neurologic deficits, mice with deletions of CD8 showed minimal or no deficits despite demyelination. In all strains, deletion of CD4 but not CD8 resulted in a decreased delayed-type hypersensitivity response to viral antigen. We conclude that each T-cell subset makes a discrete and nonredundant contribution to protection from viral persistence and demyelination in resistant strains. In contrast, in susceptible strains, CD8⁺ T cells do not provide protection against chronic demyelinating disease. Furthermore, in persistent TMEV infection of the central nervous system, neurologic deficits appear to result either from the absence of a protective class II-restricted immune response or from the presence of a pathogenic class I-restricted response.Multiple sclerosis (MS) is the most common demyelinating disease of the central nervous system (CNS) in humans. MS lesions are characterized by foci of inflammation, myelin destruction, and formation of astrocytic scars known as plaques. The presence of CD4⁺ T cells, CD8⁺ T cells (11), and macrophages in lesions suggests that pathogenesis is immunologically mediated; however, the specific contribution of specific cell types remains unknown (12, 44, 45). Although the etiology of MS is unknown, virus infection is the only epidemiological factor consistently associated with clinical exacerbation (43), and beta interferon, a cytokine with multiple known antiviral properties (46), is the only therapeutic agent definitively shown to decrease exacerbation and limit disability in MS (46). Therefore, the study of viral models of demyelination is extremely relevant.Theiler’s murine encephalomyelitis virus (TMEV), a picornavirus, induces a pathological and clinical disease similar to MS (24). Intracerebral infection with the Daniel strain (DA) of TMEV induces transient, acute neuronal polioencephalitis followed by chronic white matter demyelination and neurologic deficits in mice with susceptible (H-2^f,p,q,r,s,v) major histocompatibility complex (MHC) haplotypes (15, 32). Mice with resistant (H-2^b,d,k) MHC haplotypes recover from the acute disease with no obvious long-term sequelae or demyelination. Although TMEV infection of severely immunodeficient SCID mice results in severe neuronal encephalitis and death within approximately 2 weeks, these mice do not develop demyelination in the spinal cord white matter (38). However, when the immune systems of SCID mice are reconstituted by the adoptive transfer of splenocytes from immunocompetent mice or splenocytes treated with antibodies to CD4 or CD8, infection with TMEV results in chronic demyelination (38). These data indicate that similar to human MS, myelin destruction in chronic TMEV infection is immunologically mediated and requires contributions from both CD4⁺ and CD8⁺ T cells.Various reports have implicated both MHC class I- and class II-restricted cells in the pathogenesis of TMEV infection. CD4⁺ T cells have been implicated by studies demonstrating that demyelination is decreased following treatment with antibodies to CD4 (47) or I-A (34), is increased by adoptive transfer of a CD4⁺ T-cell line specific for VP2 capsid protein (9), and, in some studies, correlates with the development of a CD4-mediated delayed-type hypersensitivity (DTH) response against virus antigen (5). Furthermore, β₂-microglobulin-deficient mice, which are deficient in MHC class I, CD8⁺ T cells, and natural killer cells, develop demyelinating disease (6, 16, 28). In contrast, a role for CD8⁺ T cells has been suggested by studies demonstrating that susceptibility to demyelination maps genetically to MHC class I (H-2D) (1, 35), differential expression of MHC class I in the CNS correlates with disease susceptibility (1), and depletion of CD8⁺ T cells diminishes demyelination (41). Myelin destruction and neurologic deficits develop in TMEV-infected Aβ⁰ mice which are deficient in functional MHC class II and CD4⁺ T cells (20). Of interest, both class I and class II-deficient mice share the resistant (H-2^b) haplotype. This suggests that although multiple studies have implicated CD4⁺ and CD8⁺ T cells in the pathogenesis of TMEV infection, each of these components of the immune response is independently required for maintenance of resistance to demyelination.In order to definitively establish the contribution of CD4⁺ and CD8⁺ T cells to demyelination and neurologic deficits, mice lacking surface expression of CD4 or CD8 were backcrossed onto genetically resistant C57BL/6 (H-2^b) and susceptible SJL (H-2^s) and PLJ (H-2^u) strains. In this report, we confirm that both CD4⁺ and CD8⁺ T cells are required for protection from viral persistence and demyelination in resistant strains of mice. We also demonstrate that genetic deletion of CD8 does not significantly affect the degree of demyelination or survival in susceptible strains; however, genetic deletion of CD4 greatly increases the degree of demyelination and worsens clinical disease. Of interest, genetic deletion of CD8 greatly reduces neurologic deficits in animals with demyelination.     

Morphometric study of the genus Panstrongylus Berg, 1879 (Hemiptera, Reduviidae, Triatominae)

The subfamily Triatominae is actually represented by 137 species distributed among 6 tribes and 19 genera. Within this subfamily, the genus Panstrongylus, Berg 1879, is composed by 13 species widespread in sylvatic, peridomestic, and domestic habitats of Neotropical regions. These species are vectors of Chagas disease and consequently are found associated with its main hosts, such as birds and mammals. Interest in species of this genus has been increasing in the last few years. Reports of several authors indicate these Triatominae to invade and colonize houses, increasing their epidemiological significance. Morphometry was used in this study to investigate correlations among possible closely related species. We measured 224 specimens among 13 species through a set of metric variables of the head. The results indicated that the genus Panstrongylus seems to be homogeneous since 10 of the 14 species were shown to be closely related.     

Hybridization and speciation

Hybridization has many and varied impacts on the process of speciation. Hybridization may slow or reverse differentiation by allowing gene flow and recombination. It may accelerate speciation via adaptive introgression or cause near‐instantaneous speciation by allopolyploidization. It may have multiple effects at different stages and in different spatial contexts within a single speciation event. We offer a perspective on the context and evolutionary significance of hybridization during speciation, highlighting issues of current interest and debate. In secondary contact zones, it is uncertain if barriers to gene flow will be strengthened or broken down due to recombination and gene flow. Theory and empirical evidence suggest the latter is more likely, except within and around strongly selected genomic regions. Hybridization may contribute to speciation through the formation of new hybrid taxa, whereas introgression of a few loci may promote adaptive divergence and so facilitate speciation. Gene regulatory networks, epigenetic effects and the evolution of selfish genetic material in the genome suggest that the Dobzhansky–Muller model of hybrid incompatibilities requires a broader interpretation. Finally, although the incidence of reinforcement remains uncertain, this and other interactions in areas of sympatry may have knock‐on effects on speciation both within and outside regions of hybridization.     

Pathogenesis of Primary Foot-and-Mouth Disease Virus Infection in the Nasopharynx of Vaccinated and Non-Vaccinated Cattle

A time-course pathogenesis study was performed to compare and contrast primary foot-and-mouth disease virus (FMDV) infection following simulated-natural (intra-nasopharyngeal) virus exposure of cattle that were non-vaccinated or vaccinated using a recombinant adenovirus-vectored FMDV vaccine. FMDV genome and infectious virus were detected during the initial phase of infection in both categories of animals with consistent predilection for the nasopharyngeal mucosa. A rapid progression of infection with viremia and widespread dissemination of virus occurred in non-vaccinated animals whilst vaccinated cattle were protected from viremia and clinical FMD. Analysis of micro-anatomic distribution of virus during early infection by lasercapture microdissection localized FMDV RNA to follicle-associated epithelium of the nasopharyngeal mucosa in both groups of animals, with concurrent detection of viral genome in nasopharyngeal MALT follicles in vaccinated cattle only. FMDV structural and non-structural proteins were detected in epithelial cells of the nasopharyngeal mucosa by immunomicroscopy 24 hours after inoculation in both non-vaccinated and vaccinated steers. Co-localization of CD11c⁺/MHC II⁺ cells with viral protein occurred early at primary infection sites in vaccinated steers while similar host-virus interactions were observed at later time points in non-vaccinated steers. Additionally, numerous CD8⁺/CD3^- host cells, representing presumptive natural killer cells, were observed in association with foci of primary FMDV infection in the nasopharyngeal mucosa of vaccinated steers but were absent in non-vaccinated steers. Immunomicroscopic evidence of an activated antiviral response at primary infection sites of vaccinated cattle was corroborated by a relative induction of interferon -α, -β, -γ and -λ mRNA in micro-dissected samples of nasopharyngeal mucosa. Although vaccination protected cattle from viremia and clinical FMD, there was subclinical infection of epithelial cells of the nasopharyngeal mucosa that could enable shedding and long-term persistence of infectious virus. Additionally, these data indicate different mechanisms within the immediate host response to infection between non-vaccinated and vaccinated cattle.     

Biotransformations of Bile Acids with Bacteria from Cayambe Slaughterhouse (Ecuador): Synthesis of Bendigoles

The biotransformations of cholic acid ( 1a ), deoxycholic acid ( 1b ), and hyodeoxycholic acid ( 1c ) to bendigoles and other metabolites with bacteria isolated from the rural slaughterhouse of Cayambe (Pichincha Province, Ecuador) were reported. The more active strains were characterized, and belong to the genera Pseudomonas and Rhodococcus. Various biotransformation products were obtained depending on bacteria and substrates. Cholic acid ( 1a ) afforded the 3‐oxo and 3‐oxo‐4‐ene derivatives 2a and 3a (45% and 45%, resp.) with P. mendocina ECS10, 3,12‐dioxo‐4‐ene derivative 4a (60%) with Rh. erythropolis ECS25, and 9,10‐secosteroid 6 (15%) with Rh. erythropolis ECS12. Bendigole F ( 5a ) was obtained in 20% with P. fragi ECS22. Deoxycholic acid ( 1b ) gave 3‐oxo derivative 2b with P. prosekii ECS1 and Rh. erythropolis ECS25 (20% and 61%, resp.), while 3‐oxo‐4‐ene derivative 3b was obtained with P. prosekii ECS1 and P. mendocina ECS10 (22% and 95%, resp.). Moreover, P. fragi ECS9 afforded bendigole A ( 8b ; 80%). Finally, P. mendocina ECS10 biotransformed hyodeoxycholic acid ( 1c ) to 3‐oxo derivative 2c (50%) and Rh. erythropolis ECS12 to 6α‐hydroxy‐3‐oxo‐23,24‐dinor‐5β‐cholan‐22‐oic acid ( 9c , 66%). Bendigole G ( 5c ; 13%) with P. prosekii ECS1 and bendigole H ( 8c ) with P. prosekii ECS1 and Rh. erythropolis ECS12 (20% and 16%, resp.) were obtained.     

Spatial and temporal coordination of traction forces in one-dimensional cell migration

ABSTRACT

Migration of a fibroblast along a collagen fiber can be regarded as cell locomotion in one-dimension (1D). In this process, a cell protrudes forward, forms a new adhesion, produces traction forces, and releases its rear adhesion in order to advance itself along a path. However, how a cell coordinates its adhesion formation, traction forces, and rear release in 1D migration is unclear. Here, we studied fibroblasts migrating along a line of microposts. We found that when the front of a cell protruded onto a new micropost, the traction force produced at its front increased steadily, but did so without a temporal correlation in the force at its rear. Instead, the force at the front coordinated with a decrease in force at the micropost behind the front. A similar correlation in traction forces also occurred at the rear of a cell, where a decrease in force due to adhesion detachment corresponded to an increase in force at the micropost ahead of the rear. Analysis with a bio-chemo-mechanical model for traction forces and adhesion dynamics indicated that the observed relationship between traction forces at the front and back of a cell is possible only when cellular elasticity is lower than the elasticity of the cellular environment.     

Chromosomal location of the active NORs in theSteropleurus martorelli complex

The chromosomal location of the active NORs has been analyzed by a silver impregnation procedure in theSteropleurus martorelli complex. A primary NOR, which is always present at the first meiotic prophase, has been found in each of the four described races. In addition to this, all races possess one or two secondary NORs which are less active than the former and can be occasionally shown. Usually only one of the two homologous chromosomes has been found to be involved with nucleolus organisation.These results are discussed in relation to hypotheses on the chromosome differentiation of this species complex.