Depletion of alveolar macrophages in CD11c diphtheria toxin receptor mice produces an inflammatory response.

Alveolar macrophages play a critical role in initiating the immune response to inhaled pathogens and have been shown to be the first cell type infected following intranasal inoculation with several pathogens, including Francisella tularensis. In an attempt to further dissect the role of alveolar macrophages in the immune response to Francisella, we selectively depleted alveolar macrophages using CD11c.DOG mice. CD11c.DOG mice express the diphtheria toxin receptor (DTR) under control of the full CD11c promoter. Because mice do not express DTR, tissue restricted expression of the primate DTR followed by treatment with diphtheria toxin (DT) has been widely used as a tool in immunology to examine the effect of acute depletion of a specific immune subset following normal development. We successfully depleted alveolar macrophages via intranasal administration of DT. However, alveolar macrophage depletion was accompanied by many other changes to the cellular composition and cytokine/chemokine milieu in the lung that potentially impact innate and adaptive immune responses. Importantly, we observed a transient influx of neutrophils in the lung and spleen. Our experience serves as a cautionary note to other researchers using DTR mice given the complex changes that occur following DT treatment that must be taken into account when analyzing data.

Maturation defective myeloid dendritic cells in nonalcoholic fatty liver disease patients release inflammatory cytokines in response to endotoxin.

PURPOSE: Nonalcoholic fatty liver disease (NAFLD) is characterized by the presence of elevated circulating endotoxin levels. The continuous presence of endotoxin might be responsible for inducing activation of the innate immune system resulting in chronic sub-clinical inflammation. This study examines the status of dendritic cells (DCs), an important component of innate immune system, in patients with NAFLD. METHODS: Effect of lipopolysaccharide (LPS) stimulation on maturation and activation of monocyte derived dendritic cells (mo-DCs) was evaluated in ten patients with NAFLD using flow cytometry, endocytosis assay, cytokine assay and mixed leukocyte reaction. RESULTS: Although the frequency of mo-DCs in NAFLD patients was similar to that of healthy controls, there was no upregulation in levels of HLA-DR, CD83, CD80 and CD86 on their surface in response to LPS stimulation ex vivo. Although the mo-DC from patients had higher endocytosing and lower allostimulatory capacities as compared to healthy controls indicating maturation defects yet they secreted significantly high amount of TNF-α and IL-6 suggesting higher activation state. CONCLUSIONS: Our results indicate that DCs in patients with NAFLD exhibit immature yet functionally activated phenotype in response to LPS stimulation as they secrete inflammatory cytokines which further contribute in exacerbating the symptoms. Inefficient antigen presentation in these patients might add another parameter while looking at the severity of disease.

Success of antiviral therapy in chronic hepatitis C infection relates to functional status of myeloid dendritic cells.

Chronic hepatitis C infection poses a major global health predicament and appears to be potent threat to mankind. The treatment in wide use is interferon/ribavirin combination therapy which is generally effective in about 60-70 per cent of patients carrying genotype 3 and causes significant morbidity. The response to therapy is largely guided by limited number of factors such as genotype of virus, rapid virological response, ethnicity, pre-therapy viral load, etc. While involvement of host genetic factors has been a major focus of research in playing an important role in the outcome of disease, the role of immune system cannot be marginalized. Poor cellular trafficking and suboptimal T cell responses in liver, the hall marks of chronic hepatitis C virus infection, might be attributed to defective antigen presentation. Various immunological factors, both innate and adaptive, play role in the pathogenesis of the disease and become dysfunctional in active disease. Recent reports suggest the major impact of functional and numerical status of dendritic cells in deciding the fate of antiviral therapy. In this review we take a look at the involvement of dendritic cells in playing an important role in the response to therapy.

Functional reconstitution of defective myeloid dendritic cells in chronic hepatitis C infection on successful antiviral treatment.

OBJECTIVE: Poor cellular trafficking and suboptimal T-cell responses in liver, the hall marks of chronic hepatitis C virus (CHC) infection, might be attributed to defective antigen presentation. Controversy exists regarding role of myeloid dendritic cells (DCs) in CHC and response to antiviral treatment. This study examines functional status of DCs before and after completion of treatment with the aim to find any modulatory effect. DESIGN: Frequency and functions of monocyte-derived DCs (mo-DCs) were evaluated in CHC (n = 25), before the start of therapy (CHC(0) ). These patients were then put on treatment with peg-interferon-α plus ribavirin for 24 or 48 weeks, and the mo-DC functions were evaluated after 6 months of completion of treatment (CHC(6) ) again, using multicolour flow cytometry, endocytosis assay, cytokine assay and mixed lymphocyte reaction. RESULTS: Pre-treatment frequency of mo-DCs in CHC(0) was lower than that in healthy controls, which became close to normal in patients who achieved virological response (SVR+, n = 20) but not in non-responders (SVR-, n = 5). Pre-treatment levels of CD83, CD80 and CD86 on mo-DC in SVR(0) +, but not SVR(0) -, got upregulated after lipopolysaccharide stimulation supporting the hypothesis that DCs play deciding role in response to therapy. Post-treatment allostimulatory and phagocytosing capacity of mo-DCs in SVR+ patients indicated regain in functional capacity in these patients but not in SVR- patients. CONCLUSIONS: Our results indicate that DCs in CHC patients exhibiting mature and functional phenotype prior to therapy achieve sustained virological response suggesting that functional modulation of defective DCs is directly associated with successful response to therapy.

HBV specific T-cell responses in hepatitis B.

BACKGROUND: Cellular immune responses seem to prevail in acute hepatitis, whereas chronically infected patients demonstrate generally suppressed cellular immune responses and significantly greater antibody responses. AIM: To study hepatitis B virus (HBV) specific T cell proliferative responses in HBV related liver diseases. METHODS: We analyzed the T lymphocyte proliferative responses to the nonspecific mitogen phytohemagglutinin (PHA) and the HBV specific hepatitis B core antigen (HBcAg) by calculating T cell proliferation index in 10 acute viral hepatitis (AVH) patients, 19 chronic hepatitis B (CHB) patients, 10 HBV cirrhotics, 10 inactive carriers and 10 healthy controls using MTT assay. RESULTS: The mean proliferation index (PI) to PHA was highest in healthy controls (133.2 +/- 58.1) and lowest in cirrhotics (44.1 +/- 46.9) with all other groups falling in between. On comparing the mean T cell responses to HBcAg, AVH patients had the highest mean response (186.48 +/- 116.37) followed by CHB (137.9 +/- 134.3), inactive carriers (63.2 +/- 41.2) and cirrhotics (55.5 +/- 42.7). CONCLUSIONS: Patients with AVH had the highest T cell response to HBcAg, which probably explains the clearance of virus in these patients, in contrast to patients with cirrhosis who had the lowest T cell response.