Adhesion molecules and pregnancy maintenance
Immune tolerance of the fetus is necessary for a successful pregnancy. The use of mAbs to block LFA-1 in mice prevents fetal rejection, suggesting a prominent role for adhesion molecules in the pregnancy outcome. Blois et al. (p. 1820 ) studied the effect of 24-h sound stress at gestational day (g.d.) 5.5 on CBA/J females mated with either DBA/2J males (abortion-prone mating combination) or with BALB/c males (low abortion mating). Only females of the abortion-prone combination exhibited a higher abortion rate and an increase in ICAM-1 on uterine cells; they also had an increase of the ICAM-1 ligand, LFA-1+, on cells in the uterus and placenta 4 days later (g.d. 10.5). Uterine cells from abortion-prone females had a shift to a Th1 > Th2 cytokine profile, decreased mRNA expression of T cell-inhibiting indoleamine 2, 3-dioxygenase, fewer CD4+CD25+ Treg cells and lower production of male Ag-blocking asymmetric IgG Abs. These changes in tolerance mechanisms were reversed by injection of mAbs to ICAM-1 and LFA-1 between g.d. 2.5 and 6.5. The mAbs also blocked the increased migration of macrophages, CD8α dendritic cells, TCR-γδ T cells, and CD4+CD25− T cells into the uteri of the abortion-prone mice. Adoptively transferred CFSE-labeled LFA-1+ cells from stressed abortion-prone females migrated to the uteri of unstressed abortion-prone females and induced changes similar to those seen in the abortion-prone stressed animals; no changes were noted after transfer of the cells into females of the low abortion mating. The authors conclude that ICAM-1/LFA-1 cross talk during implantation can disrupt pregnancy in stressed, abortion-prone mice.
CCR8 and IL-10 in Schistosoma mansoni infections
Chensue et al. previously reported that mice deficient in CCR8 had aberrant Th2 immune responses to Schistosoma mansoni soluble egg Ag (SEA) immobilized on beads. In an extension of their work, Freeman et al. (p. 1962 ) used the same model of lung granuloma formation to determine the mechanism by which CCR8 influences Th2 responses. CD4+ T cells producing IL-4 and IL-10, isolated from draining mediastinal lymph nodes using reagents that bound the cytokines, were dominant in an anamnestic response of mice to SEA. CCR8 transcription was highest in the IL-10+ cells. Depletion of either CD25+ or CD44+ cells from the purified IL-10+ T cell population resulted in a severe reduction in IL-10 and CCR8 transcripts in the remaining cells as determined by quantitative RT-PCR. The CD25+-depleted IL-10+ cell population did not express transcription factor Foxp3. Naive mice injected with SEA-sensitized IL-10+CD4+ T cells before challenge with SEA-beads developed granulomas with fewer eosinophils than naive controls injected with total SEA-sensitized CD4+ T cells. IL-10, IL-5, and IL-13 levels were lower in draining lymph nodes from SEA-stimulated CCR8−/− mice compared with wild-type animals. SEA-sensitized CCR8−/− mice, adoptively transferred with SEA-sensitized CD4+CCR8+/+ T cells, had granuloma eosinophil numbers and IL-5 and IL-13 levels equal to those of wild-type mice; only the eosinophil increase was lost by depletion of IL-10+ cells before transfer. CCL1, the ligand for CCR8, was found in lungs but not in draining lymph nodes of SEA-sensitized mice. The authors describe an IL-10-secreting CD44+CD25+CD4+CCR8+ T cell population arising in the lung in response to S. mansoni egg Ag challenge.
TLR4 expression on liver dendritic cells
Interaction of LPS with its receptor, TLR4, induces maturation of dendritic cells (DCs) that activate naive T cells. Although liver DC progenitors have tolerogenic properties that result in acceptance of liver allografts, there is no information about their TLR4 expression level. De Creus et al. (p. 2037 ) cultured liver and spleen mouse DCs overnight with a low level (10 ng/ml) of LPS. CD8α− and CD8α+ hepatic DCs were less able to activate allogeneic T cells in vitro than the same subtypes of splenic DCs; they also had lower levels of TLR4 mRNA and reduced surface expression of three molecules (MHC class II, CD80, and CD86). Higher T cell stimulatory activity and increased expression of the surface molecules were seen for liver DCs incubated with a higher concentration (100 ng/ml) of LPS. However, the levels were lower than in spleen DCs. Restimulated T cells, activated by liver DCs incubated with the low LPS concentration, produced low levels of IFN-γ and IL-4 and were hyporesponsive to proliferation in MLR. Incubation of liver DCs with the high LPS concentration induced a skewed Th2 response. Liver DCs from mice injected i.v. with 10 ng or 1 μg LPS were poor allogeneic T cell stimulators ex vivo. Hyporesponsiveness was induced in allogeneic T cells isolated from draining lymph nodes of mice injected s.c. with liver DCs stimulated with low dose LPS in vitro. The results show that low expression of TLR4 on liver DCs results in impaired ability to stimulate allogeneic T cells in vivo or in vitro.
Ag processing in cell-based tumor vaccines
The laboratory of Ostrand-Rosenberg developed murine vaccines consisting of invariant chain-negative tumor cells genetically modified to express both MHC class II and costimulatory molecules. These cell-based vaccines directly present endogenous tumor peptides to CD4+ T cells, thus bypassing dendritic cells. To determine the pathway by which tumor peptides are loaded onto MHC class II molecules, Dissanayake et al. (p. 1811 ) generated TAP-positive and TAP-negative mouse melanoma cell transfectants that lack invariant chain and DM molecule expression. The cells were cotransfected with vectors separately expressing an MHC class II molecule and hen egg white lysozyme (HEL) modified to localize to the endoplasmic reticulum or to the cytoplasm. T cell hybridomas specific for three different HEL peptides reacted with both the TAP-positive and TAP-negative lines regardless of localization of HEL. Treatment of acid-stripped transfectants with inhibitiors of proteasome activity or autophagy did not impair the ability of the cells to present HEL peptides. In contrast, acid-stripped transfectants treated with an inhibitor of endosomal processing had reduced presentation of HEL peptides. MHC class II molecules were detected in endosomal compartments by confocal microscopy, and vaccine cells were shown to release, but not endocytose, HEL peptides. The authors conclude that MHC class II presentation of endogenous peptides from either the cytosol or endoplasmic reticulum occurs through an endosomal pathway that does not involve TAP or the proteasome.
Protecting neurons against C damage
Tissue damage in inflammatory diseases of the CNS is due in part to C-mediated cell death. However, it is not known whether endogenous C regulatory proteins have a role in limiting neuronal damage. van Beek et al. (p. 2353 ) examined neuronal damage in a marmoset model of chronic experimental autoimmune encephalomyelitis (EAE), similar to human multiple sclerosis, and in a rhesus monkey model of acute EAE, resembling human postinfectious encephalomyelitis. Immunostaining for C1q and C3b was strong in brain tissue from both models, although the staining pattern was specific to the model and was found in areas of inflammatory infiltrates. Membrane-bound C regulatory proteins CD35, CD59, CD46, and CD55 were overexpressed at sites of inflammatory infiltrates in EAE pathology. CD55 (decay accelerating factor) expression was strong on inflammatory infiltrates and adjacent neurons in marmoset EAE brains but not in control brains; these areas costained for C3 opsonin. Rhesus EAE brains expressed CD55 only on infiltrating cells. Human neuronal cell lines expressed low levels of CD55, which was localized to lipid rafts in one cell line transfected with a plasmid expressing CD55. Cross-linking cell surface CD55 increased tyrosine phosphorylation on four neuronal proteins, and CD55-expressing cells were protected against C-mediated lysis even in the presence of Ab against CD59. The authors conclude that C opsonins are involved in neuronal damage in both EAE models and that the neuronal membrane overexpresses the C regulator CD55 to limit damage in the chronic condition.
An effective botulism vaccine
Bioterrorism presents a challenge for immunization against agents such as Clostridium botulinum neurotoxin (BoNT) which most likely would be delivered by aerosol or in contaminated food or water. Parenteral administration of vaccines usually does not elicit protective mucosal immune responses. Kobayashi et al. (p. 2190 ) found that injection of mice with BoNT type A Toxoid (BoNToxoid/A), plus a mutant of cholera toxin (mCT) as adjuvant, induced significant secretory IgA (S-IgA) Ab responses in saliva, nasal washes, and fecal specimens as measured in BoNT/A-specific ELISA. Minimal S-IgA Ab responses were elicited by injection of toxoid without mCT. Only mice vaccinated with the toxoid plus mCT had high levels of BoNT/A-specific plasma IgG Abs of several subclasses and large numbers of BoNT/A-specific IgA and IgG Ab-forming cells in nasal passages and spleen; BoNT/A-specific IgA Ab-forming cells were found in intestinal lamina propria. Mice vaccinated with the toxoid and mCT weekly for 4 wks survived i.p. or mucosal challenge with a lethal dose of BoNT/A, whereas all mice vaccinated with toxoid alone died within 24 h of challenge by either route. One-third of mice injected with BoNT/A plus fecal extracts from mice vaccinated with toxoid plus mCT survived for 7 days, whereas 75% of mice injected with BoNT/A plus fecal extracts from mice vaccinated with toxoid alone died within 1 day. The study shows that nasal administration of BoNToxoid/A plus mCT as adjuvant induces protective systemic and mucosal immunity to parenteral or oral administration of lethal doses of BoNT/A.
Eliminating HIV-1-specific CD4+ T cells
Virus-specific CD4+ T cells control viral infections. However, virus-specific CD4+ T cells in HIV-1-infected individuals are reduced in number and have poor proliferative responses to viral Ag. To explain the loss of these T cells during HIV-1 infection, Yue et al. (p. 2196 ) characterized CMV-specific CD4+ T cells and HIV-1-specific CD4+ T cells from the same HIV-1-infected individuals. Ex vivo stimulation of the cells with the appropriate viral Ag resulted in IFN-γ production in 23% of the CMV-specific cells vs 1.6% of the HIV-1-specific cells. Higher levels of activated caspase 3 and enhanced TUNEL staining were seen in the HIV-1-specific cells. A negative correlation between cell count and percentage of apoptotic cells was seen only for the HIV-1-specific CD4+ T cells. A high HIV-1 count correlated positively with percentage of CD4+ T cell apoptosis. Slow or long term nonprogressors or individuals who received highly active antiretroviral therapy for 6 mo had low levels of caspase 3 activation comparable to those of CMV-specific CD4+ T cells. HIV-1 specific CD4+ T cells were not susceptible to anti-CD95 Ab-induced apoptosis; however, lower levels of Bcl-2 were seen in HIV-1 chronic progressors. Pretreatment of HIV-1-specific CD4+ T cells with an inhibitor of caspase-3 or caspase-9 or with a free radical oxygen scavenger resulted in enhanced Ag-specific IFN-γ responses. The authors conclude that loss of HIV-1-specific CD4+ T cells is a result of mitochondrial apoptosis induced by HIV-1 Ag.
Summaries written by Dorothy L. Buchhagen, Ph.D.