Immune effector mechanism in parasitic infections

In this article is a summary of our recent findings on the role of nitric oxide (NO) as an effector mechanism against the intracellular parasite, Leishmania major. NO is produced in large amounts in murine macrophages following activation by IFNgamma synthesized by Th1 cells. NO production is inhibited by IL-4, a product of Th2 cells. A set of stable cell surface markers has now been identified. ST2L and IL-18R are selectively expressed on Th2 and Th1 cells respectively. Antibody against ST2L can down-regulate Th2 cells in the highly susceptible BALB/c mice leading to control of otherwise fatal L. major infection. These results show directly the critical role of the balance between Th1 and Th2 cells in cutaneous leishmaniasis.     

Comparison of the expression of p53, p21, Bax and the induction of apoptosis between patients with basal cell carcinoma and normal controls in response to ultraviolet irradiation

AIM: Ultraviolet light (UV) is known to cause DNA damage in the epidermis. The damaged DNA is repaired or deleted by apoptosis to prevent the generation of cancer. It has been suggested that a deficient apoptotic mechanism may predispose individuals to skin cancer. Therefore, the response of normal controls and patients with basal cell carcinoma (BCC) to UV irradiation was investigated. METHODS: The buttock skin from normal volunteers and patients with BCC was irradiated using solar simulated radiation (SSR). SSR mimics the effect of natural sunlight. Skin biopsies were excised and examined for p53, p21, and Bax protein expression and for the induction of apoptosis. RESULTS: At 33 hours after UV irradiation, the induction of apoptosis was significantly higher (p = 0.04) in patients with BCC than in normal volunteers (Mann Whitney test). A trend towards higher p21 expression was found at 33 hours in patients with BCC (mean, 18.69 positive cells/field) than in normal volunteers (mean, 9.89), although this difference was not significant (p = 0.05 positive cells/field). CONCLUSION: These results may imply that patients with BCC have enhanced sensitivity to UV irradiation or that there is some defect in the cell arrest or repair pathways, which results in damaged cells been pushed into apoptosis rather than repair.     

The PTPN22 R620W polymorphism associates with RF positive rheumatoid arthritis in a dose-dependent manner but not with HLA-SE status

We have recently described the association between rheumatoid arthritis and a coding single-nucleotide polymorphism in the intracellular protein tyrosine phosphatase, PTPN22. The disease-associated polymorphism, 1858 C/T (rs2476601), encodes an amino-acid change (R620W) in one of four SH3 domain binding sites in the PTPN22 molecule. We have now extended our initial studies to address three questions: (1) Is the association with rheumatoid arthritis limited to rheumatoid factor (RF) positive disease? (2) Does homozygosity for PTPN22 R620W substantially increase disease susceptibility? (3) Is there an interaction between PTPN22 and the rheumatoid arthritis (RA)-associated HLA-DRB1 shared epitope alleles? A total of 1413 Caucasian rheumatoid arthritis patients and 1401 Caucasian controls were genotyped. The results support the view that PTPN22 was strongly and preferentially associated with RF positive disease (OR=1.75, 95% CI 1.46-2.10, P=1.3 x 10(-9)). The PTPN22 risk allele was not significantly associated with RF negative disease (OR=1.19, 95% CI 0.92-1.53, P=0.18), although a very weak association cannot be completely excluded. There was a strong dose effect on disease risk; two copies of the PTPN22 R620W allele more than doubles the risk for RF positive RA (OR=4.57, 95% CI 2.35-8.89). There was no evidence of a genetic association between PTPN22 and HLA susceptibility alleles.     

Pre-exposure of murine macrophages to lipopolysaccharide inhibits the induction of nitric oxide synthase and reduces leishmanicidal activity

Murine macrophages produce nitric oxide (NO) from L-arginine on stimulation with lipopolysaccharide (LPS), alone or with interferon-γ (IFN-γ). The effect of incubation of macrophages with low concentrations of LPS on NO synthesis on subsequent stimulation was investigated, using a murine macrophage cell line, J774, and peritoneal macrophages from CBA mice. Cells which had been incubated with LPS produced significantly lower amounts of NO, and expressed lower levels of NO synthase activity, following stimulation with IFN-γ and LPS, or with a high concentration of LPS. This effect was not reversed by tumor necrosis factor-α. The ability of CBA macrophages to kill the intracellular parasite Leishmania major was markedly reduced by pre-incubation with LPS. Reduced NO production by macrophages previously exposed to LPS is a manifestation of endotoxin tolerance, and may represent an important means of regulation of NO synthesis and thus a survival mechanism for intracellular parasites.     

A novel negative regulator for IL-1 receptor and Toll-like receptor 4

The Toll-IL-1 receptor (TIR) superfamily, defined by the presence of an intracellular TIR domain, initiates innate immunity via NF-kappaB activation, leading to production of proinflammatory cytokines. ST2 is a member of the TIR family that does not activate NF-kappaB and has been suggested as an important effector molecule of type 2 T helper cell responses. We have recently demonstrated that the membrane bound form of ST2 (ST2L) negatively regulated IL-1RI and TLR4 but not TLR3 signaling by sequestrating the adaptors MyD88 and Mal. In contrast to wild-type mice, ST2 deficient mice failed to develop endotoxin tolerance. Thus, ST2 suppresses IL-1R and TLR4 signaling via MyD88- and Mal-dependent pathways and modulates innate immunity. The results provide a molecular explanation for the role of ST2 in T(H)2 responses since inhibition of TLRs will promote a T(H)2 response and also identify ST2 as a key regulator of endotoxin tolerance.     

Regulation of delayed-type hypersensitivity. II. Specific suppressor factor for delayed-type hypersensitivity to sheep erythrocytes in mice.

An antigen-specific suppressor factor for delayed-type hypersensitivity (DTH) to sheep red blood cells (SRBC) in mice is described. Lymph node cells and spleen cells from mice injected intravenously with 1 x 10(9) SRBC 4 days previously were incubated in vitro for 48 h in culture medium. Supernatant obtained from the culture inhibited the induction of DTH to SRBC in normal mice. It also suppressed the expression of DTH in presensitized mice. The suppression is specific as the suppressor factor had no effect on the DTH to noncross-reacting antigen, chicken red blood cells. Treatment of the spleen cells with anti-theta serum and complement prevented the production of the suppressor factor, whereas treatment with anti-Ig serum and complement had no effect. Suppressor factor produced by H-2k mice suppressed the DTH in H-2b mice. The factor thus seems to act across the H-2 barrier. The suppressor factor was not removed by adsorption with goat anti-mouse immunoglobulin immunoadsorbent, but could be adsorbed by SRBC. It was stable at 56 degrees C for 1 h, but was partially inactivated by freezing and thawing. The factor has a molecular weight of less than 35 000 daltons.     

Identification of four distinct regions of allelic imbalances on chromosome 1 by the combined comparative genomic hybridization and microsatellite analysis on hepatocellular carcinoma.

Frequent chromosome 1 abnormalities detected in human hepatocellular carcinoma have been implicated in early genetic events of liver carcinogenesis. Recurrent loss of 1p with a common deleted region 1p36-p34 has been reported from microsatellite analysis, whereas common gain of the whole chromosome q-arm was described from several comparative genomic hybridization studies. The relationships between copy number changes and allelic status however remains unclear. In this study, we have conducted a simultaneous comparative genomic hybridization and microsatellite analysis study on chromosome 1 in 31 hepatocellular carcinoma cases. Microsatellite analysis revealed frequent loss of heterozygosity on 1p at loci D1S468 (74%), D1S450 (67%), D1S2667 (65%), D1S2697 (75%), D1S199 (52%), and D1S234 (67%) corresponded to the distal 1p36 region and coincided with 12 cases (86%) that presented losses on 1p by comparative genomic hybridization analysis. Although comparative genomic hybridization indicated a common deleted region of 1p36-p35 in the current series, microsatellite analysis has refined the smallest overlapping region (SOR) to 1p36.13-p36.22. Gain of 1q as revealed by comparative genomic hybridization suggested low and high-level gains, and cases that displayed an amplicon below the heterochromatic region 1q21-q25. Common allelic imbalances of polymorphic markers D1S2635 (64%), D1S484 (67%), D1S2878 (65%), D1S196 (70%), D1S249 (64%) D1S2785 (75%), D1S2842 (73%) and D1S2836 (74%) that corresponded to the regions 1q23.1-q24.2, 1q32.1 and 1q43-q44 were detected. Three distinct regions of allelic imbalances were thus suggested on recurring 1q gain found in hepatocellular carcinoma. Furthermore, microsatellite analysis has enabled a mapping of common overrepresented regions and suggested SOR on 1q23.1-q23.3 (D1S2635-D1S2878), 1q25.1-q31.1 (D1S452-D1S238), and 1q43 (D1S2785-D1S2842). Our current study has refined chromosome 1 aberrations in hepatocellular carcinoma to four regions of allelic imbalances. The SORs delineated should provide basis for further molecular investigation in hepatocarcinogenesis on genes residing on these chromosomal regions.     

Regulation of ST2L expression on T helper (Th) type 2 cells

T1/ST2L, an IL-1 receptor homologue, is selectively expressed on murine Th2 cells and specific anti-ST2L antibodies can profoundly modulate the Th1/Th2 balance in vivo. Naive CD4+ T cells do not express ST2L but do so on activation with specific antigen in the presence of IL-4 or when stimulated with low doses of antigen in the absence of exogenously added IL-4. Similarly enhanced ST2L expression occurred after stimulation of Th2 cells with antigen or the mitogen ConA in the presence of APC. Restimulation of Th2 cells in the presence of IFN-gamma led to a decreased expression of ST2L to below basal levels. Conversely, Th2 cells cultured with IL-4 led to increased ST2L expression. The reduced expression of ST2L in response to high doses of antigen is also reversed by the neutralization of IFN-gamma. Using an ST2L promoter/luciferase reporter gene construct, we show that the distal but not proximal ST2L promoter is responsible for specific gene expression in Th2 cells. IL-4 enhances, whereas IFN-gamma suppresses ST2L expression via direct modulation of the distal promoter of the ST2L gene. These data provide a mechanistic explanation for the selective expression of ST2L on Th2 cells.