Clinical, morphologic, and immunohistochemical features of canine orbital hibernomas.

Hibernomas are uncommon benign tumors of brown fat that occur in humans and various animal species. They have not been observed in the orbit of dogs, humans, or other animals. Here we report clinical, light and electron microscopic, and immunohistochemical features of a series of 7 hibernomas arising in the orbital region of dogs. These neoplasms occurred in adult dogs with no breed predilection. The mean age of the affected dogs was 10.4 years (range, 8-13 years). All neoplasms presented as soft lobular masses composed of predominantly round or polygonal neoplastic cells with granular eosinophilic and vacuolated cytoplasm resembling adipocytes. The cytoplasm contained large numbers of pleomorphic mitochondria with dense matrices and indistinct cristae. Immunohistochemical evaluation confirmed positive labeling of neoplastic cells from all cases with uncoupling protein 1 (UCP-1) consistent with brown fat differentiation. Interestingly, rare neoplastic cells also expressed myogenin and myoD, possibly suggesting a common progenitor cell for neoplastic brown adipose and skeletal muscle cells.

Positive selection of EqCD8+ precursors increases equine lymphokine-activated killing.

Lymphokine activated killing (LAK) is an example of natural cytotoxicity, and as such is a critical means of defense against diseases such as viral infection and neoplasia. Despite this important role, the specific molecular interactions involved in LAK or other forms of natural cytotoxicity are only partially understood. In some species, cells capable of mediating natural cytotoxicity express the CD8 molecule, although no specific role has been demonstrated for CD8 in non-MHC restricted cytotoxicity. In this study the role of the EqCD8 equine homolog of CD8 in LAK cell activity was examined. A series of LAK assays were performed using equine lymphocyte populations enriched or depleted for EqCD8 expression by positive or negative selection. The results indicate that positive selection of LAK precursors using an anti-EqCD8 (CVS8) antibody greatly increases LAK cytotoxicity. The implications for the role of the EqCD8 molecules in LAK are discussed.

Abnormal patterns of equine leucocyte differentiation antigen expression in severe combined immunodeficiency foals suggests the phenotype of normal equine natural killer cells.

Severe combined immunodeficiency (SCID) is a fatal autosommal disease of Arabian horses that leads to failure of maturation of T- and B-lymphocyte populations, although natural killer (NK) cells are unaffected. Thymic and lymph node tissues from two foals suffering from SCID were examined in an immunohistological study using a panel of monoclonal antibodies recognising equine leucocyte differentiation antigens. In both foals, the majority of cells in lymphoid tissues had an EqCD3-EqCD4-EqCD8+ phenotype, although rare EqCD3+ cells were also detected. The EqCD3-EqCD4-EqCD8+ cells may represent an abnormal lymphocyte differentiation product resulting from the SCID defect, or alternatively may be a normal equine NK cell population. We suggest that the evidence favours the latter proposal, and that equine NK cells in normal horses therefore may be identified by an EqCD3-EqCD8+ phenotype. The implications for the nature of the equine SCID defect are discussed.

IFN-gamma-mediated antimicrobial response. Indoleamine 2,3-dioxygenase-deficient mutant host cells no longer inhibit intracellular Chlamydia spp. or Toxoplasma growth.

The role of indoleamine 2,3-dioxygenase (IDO) in IFN-gamma-mediated inhibition of intracellular parasite growth has been examined previously, although earlier work has been largely correlative. In this study, we defined more completely the role of IDO in the IFN-antimicrobial response. Two mutant cell lines, derived from ME180 cells and exhibiting reduced IDO activity (IR3B6A, IR3B6B) were characterized to determine if they retained the capacity to inhibit intracellular Chlamydia and Toxoplasma growth. Mutant cells treated with IFN-gamma exhibited reduced capacity to suppress pathogen growth. The expression of several IFN-regulated genes also was measured to confirm that the inability to inhibit pathogen growth was because of the lack of IDO. The expression of class II MHC, intracellular adhesion molecule-1, MxA, and P68 kinase genes was induced in the IFN-gamma-treated wild type ME180 cells, but was variable in the mutant cell lines, supporting the hypothesis that IFN-gamma-induced production of IDO is a key IFN-gamma-mediated antimicrobial mechanism.

Characterization of gamma interferon-mediated cytotoxicity to chlamydia-infected fibroblasts.

Addition of murine recombinant gamma interferon (IFN-gamma) to mouse fibroblast cultures infected with Chlamydia psittaci was found to induce a cytotoxic response that was dependent on the concentration of IFN-gamma added and the multiplicity of infection given. No cytotoxicity was observed for uninfected cells treated with IFN-gamma, nor did infection alone elicit cytotoxicity. Cytotoxicity was detected only if IFN-gamma was present for at least the first 18 h of a 30-h incubation period. Cytotoxic activity was not observed when infected cells were treated with 50 micrograms of chloramphenicol per ml, a drug which inhibits differentiation of infectious elementary bodies to noninfectious reticulate bodies. Cytotoxic activity was restored if addition of chloramphenicol was delayed until 18 h postinfection. Addition of 100 U of penicillin per ml to infected host cells reduced but did not abolish cytotoxic activity. Treatment of host cells with as little as 0.2 microgram of cycloheximide per ml inhibited cytotoxicity without interfering with chlamydial growth. When addition of cycloheximide was delayed until 12 h after infection and IFN-gamma treatment, cytotoxicity was restored. These data indicate that IFN-gamma functions as a cytotoxic cytokine against chlamydia-infected fibroblasts. Cytotoxicity was found to be dependent on chlamydial multiplicity of infection, differentiation of chlamydiae to the metabolically active form, and host cell protein synthesis.