Administration of Con A induces severe injury to hepatocytes in mice and is considered to be a model for human hepatitis. In the current study, we investigated the role of CD44 in Con A-induced hepatitis. Intravenous administration of Con A (20 mg/kg) caused 100% mortality in C57BL/6 CD44-knockout (KO) mice, although it was not lethal in C57BL/6 CD44 wild-type (WT) mice. Administration of lower doses of Con A (12 mg/kg body weight) into CD44 WT mice induced hepatitis as evident from increased plasma aspartate aminotransferase levels accompanied by active infiltration of mononuclear cells and neutrophils, and significant induction of apoptosis in the liver. Interestingly, CD44 KO mice injected with similar doses of Con A exhibited more severe acute suppurative hepatitis. Transfer of spleen cells from Con A-injected CD44 KO mice into CD44 WT mice induced higher levels of hepatitis when compared with transfer of similar cells from CD44 WT mice into CD44 WT mice. The increased hepatitis seen in CD44 KO mice was accompanied by increased production of cytokines such as TNF-α, IL-2 and IFN-γ, but not Fas or Fas ligand. The increased susceptibility of CD44 KO mice to hepatitis correlated with the observation that T cells from CD44 KO mice were more resistant to activation-induced cell death when compared with the CD44 WT mice. Together, these data demonstrate that activated T cells use CD44 to undergo apoptosis, and dysregulation in this pathway could lead to increased pathogenesis in a number of diseases, including hepatitis.

A safe, more sensitive, nonradioactive, neutral red uptake assay was adopted to replace the traditional 51 Cr release assay for detection of Brucella-specific cytotoxic T lymphocyte (CTL) activity. Our studies indicated that Brucella abortus strain RB51 vaccination of mice induced specific CTLs against both strain RB51-and strain 2308-infected J774.A1 macrophages but not against Listeria monocytogenes-infected J774.A1 cells. The antigenspecific cytotoxic activity was exerted by T lymphocytes but not by NK cells. CD3 ؉ CD4 ؉ T cells secreted the highest level of gamma interferon (IFN-␥) and were able to exert a low but significant level of specific lysis of Brucella-infected macrophages. They also exerted a low level of nonspecific lysis of noninfected macrophages. In contrast, CD3؉ CD8 ؉ T cells secreted low levels of IFN-␥ but demonstrated high levels of specific lysis of Brucella-infected macrophages with no nonspecific lysis. These findings indicate that B. abortus strain RB51 vaccination of mice induces specific CTLs and suggest that CD3 ؉ CD4 ؉ and CD3 ؉ CD8 ؉ T cells play a synergistic role in the anti-Brucella activity.Brucella abortus is a gram-negative, facultative intracellular bacterial pathogen that causes brucellosis in humans and cattle (4). In the infected host, B. abortus multiplies within the phagosomes of phagocytic cells (e.g., macrophages) by inhibiting the phagosome-lysosome fusion (4). Similar to most of the intracellular bacterial infections, cell-mediated immunity seems to play a critical role in protection against virulent Brucella infection, although antibodies specific for the O polysaccharide of the lipopolysaccharide can confer a certain level of protection in some host species (1, 2, 17, 31). Passive transfer assays with mice indicated that both CD4 ϩ and CD8 ϩ T-cell subsets are involved in the protective immunity to brucellosis (1, 2). One mechanism by which immune T cells confer protection from B. abortus infection is by secreting molecules such as gamma interferon (IFN-␥), which stimulates the antimicrobial activity of macrophages, allowing intracellular bacterial killing (16,35). The crucial role of IFN-␥ in resistance to Brucella infection has been demonstrated for mice by in vivo antibody neutralization experiments (35). Another mechanism of T-cellmediated immunity is the lysis of infected cells by the specific cytotoxic T lymphocytes (CTLs) (23). Present knowledge about the role of CTLs in the acquired resistance to brucellosis is limited. The development of Brucella-specific CTLs in vaccinated animals and the phenotypic and functional characterization of such CTL's have not been studied in detail. The classic CTL assay is based on determining the level of 51 Cr released from lysed target cells. Unfortunately, this assay is not very sensitive (23,24), and the use of radioactive 51 Cr in a biosafety level 3 environment restricts the usefulness of this assay in Brucella research even further. Therefore, we have developed a highly sensitive, nonradioactive assay for Brucella...

Methylosinus trichosporium OB3b (for "oddball" strain 3b) is an obligate aerobic methane-oxidizing alphaproteobacterium that was originally isolated in 1970 by Roger Whittenbury and colleagues. This strain has since been used extensively to elucidate the structure and function of several key enzymes of methane oxidation, including both particulate and soluble methane monooxygenase (sMMO) and the extracellular copper chelator methanobactin. In particular, the catalytic properties of soluble methane monooxygenase from M. trichosporium OB3b have been well characterized in context with biodegradation of recalcitrant hydrocarbons, such as trichloroethylene. The sequence of the M. trichosporium OB3b genome is the first reported from a member of the Methylocystaceae family in the order Rhizobiales.