Concomitant canine distemper, infectious canine hepatitis, canine parvoviral enteritis, canine infectious tracheobronchitis, and toxoplasmosis in a puppy.

The concomitant infections of Canine distemper virus (CDV), Canine adenovirus A types 1 (CAdV-1) and 2 (CAdV-2), Canine parvovirus type 2 (CPV-2), and Toxoplasma gondii are described in a 43-day-old mixed-breed puppy. Clinically, there were convulsions and blindness with spontaneous death; 14 siblings of this puppy, born to a 10-month-old dam, which was seropositive (titer: 1,024) for T. gondii, also died. Necropsy revealed unilateral corneal edema (blue eye), depletion of intestinal lymphoid tissue, non-collapsible lungs, congestion of meningeal vessels, and a pale area in the myocardium. Histopathology demonstrated necrotizing myocarditis associated with intralesional apicomplexan protozoa; necrotizing and chronic hepatitis associated with rare intranuclear inclusion bodies within hepatocytes; necrotizing bronchitis and bronchiolitis; interstitial pneumonia associated with eosinophilic intracytoplasmic inclusion bodies within epithelial cells; atrophy and fusion of intestinal villi with cryptal necrosis; and white matter demyelination of the cerebrum and cerebellum associated with intranuclear inclusion bodies within astrocytes. Polymerase chain reaction (PCR) amplified the partial fragments (bp) of the CDV N gene (290 bp), CPV-2c VP2 capsid protein gene (583 bp), and CAdV-1 (508 bp) and CAdV-2 (1,030 bp) E gene from urine and tissue samples. The PCR assays demonstrated that the apicomplexan protozoa observed within several organs contained DNA specific for T. gondii; genotyping revealed T. gondii type III. The findings support the characterization of concomitant infections of CDV, CAdV-1, CAdV-2, CPV-2, and T. gondii in this puppy. Further, seroreactivity to T. gondii of the dam in association with the systemic disease observed in the puppy described herein is suggestive of congenital toxoplasmosis.

Toxoplasma gondii infection in the brain inhibits neuronal degeneration and learning and memory impairments in a murine model of Alzheimer's disease.

Immunosuppression is a characteristic feature of Toxoplasma gondii-infected murine hosts. The present study aimed to determine the effect of the immunosuppression induced by T. gondii infection on the pathogenesis and progression of Alzheimer's disease (AD) in Tg2576 AD mice. Mice were infected with a cyst-forming strain (ME49) of T. gondii, and levels of inflammatory mediators (IFN-γ and nitric oxide), anti-inflammatory cytokines (IL-10 and TGF-ß), neuronal damage, and ß-amyloid plaque deposition were examined in brain tissues and/or in BV-2 microglial cells. In addition, behavioral tests, including the water maze and Y-maze tests, were performed on T. gondii-infected and uninfected Tg2576 mice. Results revealed that whereas the level of IFN-γ was unchanged, the levels of anti-inflammatory cytokines were significantly higher in T. gondii-infected mice than in uninfected mice, and in BV-2 cells treated with T. gondii lysate antigen. Furthermore, nitrite production from primary cultured brain microglial cells and BV-2 cells was reduced by the addition of T. gondii lysate antigen (TLA), and ß-amyloid plaque deposition in the cortex and hippocampus of Tg2576 mouse brains was remarkably lower in T. gondii-infected AD mice than in uninfected controls. In addition, water maze and Y-maze test results revealed retarded cognitive capacities in uninfected mice as compared with infected mice. These findings demonstrate the favorable effects of the immunosuppression induced by T. gondii infection on the pathogenesis and progression of AD in Tg2576 mice.

Cutting edge: CD40-CD40 ligand pathway plays a critical CD8-intrinsic and -extrinsic role during rescue of exhausted CD8 T cells.

CD8 exhaustion mediated by an inhibitory programmed death-1-programmed death ligand-1 (PD-L1) pathway occurs in several chronic infections, including toxoplasmosis. Although blockade of the programmed death-1-PD-L1 pathway revives this response, the role of costimulatory receptors involved in this rescue has not been ascertained in any model of CD8 exhaustion. This report demonstrates that one such costimulatory pathway, CD40-CD40L, plays a critical role during rescue of exhausted CD8 T cells. Blockade of this pathway abrogates the ameliorative effects of anti-PD-L1 treatment on CD8 T cells. Additionally, we demonstrate in an infectious disease model that CD8-intrinsic CD40 signaling is important for optimal CD8 polyfunctionality, proliferation, T-bet upregulation, and IL-21 signaling, albeit in the context of CD8 rescue. The critical role of CD40 during the rescue of exhausted CD8 T cells may provide a rational basis for designing novel therapeutic vaccination approaches.

Infection of HIV-1 transgenic mice with Mycobacterium avium induces the expression of infectious virus selectively from a Mac-1-positive host cell population.

Infection of HIV-1-transgenic mice with Mycobacterium avium, a common opportunistic pathogen in AIDS patients, was shown to result in increased tissue expression of viral specific transcripts. Moreover, by coculturing splenocytes from the transgenic animals with human T cells it was possible to demonstrate that the elevation in HIV-1 mRNA triggered by M. avium infection reflects increased production of infectious virions. Viral immune activation was also shown to correlate with a marked elevation of p24 in supernatants of ex vivo-cultured tissues and, more importantly, in systemic increases in the HIV-1 protein in plasma. Interestingly, these tissue and systemic p24 responses were found to be differentially regulated. Thus, while in vitro p24 production by cultured splenocytes increased concurrently with bacterial loads during the first 6 wk of infection, levels of the Ag in plasma actually decreased. In situ localization experiments together with FACS analysis of HIV-1-expressing splenocytes indicated that virus production is restricted largely to cells of the monocyte/macrophage lineage. Indeed, in vitro p24 expression by cells from noninfected transgenic mice was up-regulated by polyclonal stimulation of macrophages but not T cells. Together these results underscore the importance of the macrophage reservoir in persistent virus expression and establish a convenient and relevant animal model for studying the factors responsible for immune activation of HIV-1 induced by mycobacterial as well as other common coinfections encountered by AIDS patients.

Impact of prophylactic ganciclovir on bronchoalveolar lavage lymphocyte numbers and phenotypes in murine cytomegalovirus-induced reactivation of Toxoplasma pneumonia.

In a mouse model of cytomegalovirus (CMV)-induced immunosuppression, murine CMV (MCMV) infection results in reactivation of Toxoplasma pneumonia, and prophylactic but not delayed administration of ganciclovir attenuates the severity of this pneumonia. We now report that the protection observed with ganciclovir is associated with blunting of the alterations in bronchoalveolar lavage (BAL) lymphocyte numbers and phenotypes observed in untreated mice. Specifically, prophylactic ganciclovir prevents the usual drop in BAL CD4+ lymphocytes observed in the first week after MCMV injection--that is, the period of MCMV-associated immunosuppression. Furthermore, prophylactic ganciclovir markedly blunts the usual rise in BAL T lymphocytes (CD8+ > CD4+) seen later during the peak of reactivated Toxoplasma pneumonia. These findings suggest that prophylactic ganciclovir can protect animals from virus-associated opportunistic pneumonia by attenuating virus-induced changes in BAL lymphocytes and the attendant suppression of lung immunity.

Infection of human immunodeficiency virus 1 transgenic mice with Toxoplasma gondii stimulates proviral transcription in macrophages in vivo.

Human immunodeficiency virus (HIV) 1 transgenic mice expressing low or undetectable levels of viral mRNA in lymphoid tissue were infected with the intracellular protozoan Toxoplasma gondii. Exposure to this parasite resulted in an increase in HIV-1 transcript in lymph nodes, spleens, and lungs during the acute phase of infection and in the central nervous system during the chronic stage of disease. In vivo and ex vivo experiments identified macrophages as a major source of the induced HIV-1 transcripts. In contrast, T. gondii infection failed to stimulate HIV-1 transcription in tissues of two HIV-1 transgenic mouse strains harboring a HIV-1 proviral DNA in which the nuclear factor (NF) kappa B binding motifs from the viral long terminal repeats had been replaced with a duplicated Moloney murine leukemia virus core enhancer. A role for NF-kappaB in the activation of the HIV-1 by T. gondii was also suggested by the simultaneous induction of NF-kappaB binding activity and tumor necrosis factor alpha synthesis in transgenic mouse macrophages stimulated by exposure to parasite extracts. These results demonstrate the potential of an opportunistic pathogen to induce HIV-1 transcription in vivo and suggest a mechanism for the in vivo dissemination of HIV-1 by macrophages.