Nonresponsiveness against hepatitis B vaccination has been described in 4-10% of immunized subjects. We have explored the specific cell response to hepatitis B surface antigen by analyzing: PBMC proliferation, cytokine production (Th1, Th2 profiles, and TGF-beta), and activation molecules on Th cells. A poor proliferative response was demonstrated in nonresponders (P < 0.05). T cells from responders produced all tested cytokines (P < 0.01), in contrast with nonresponders subjects (P < 0.05). Expression of CD69 and CD25 was diminished in T cells from nonresponders (P < 0.01). A reduced expression of CD40L was also detected in T cells from nonresponders (P < 0.01). An elevated correlation coefficient was observed between CD40L on CD4+ cells and antibody production. These results suggest an overall inability of T cells to be activated which could be consistent with potential differences in antigen presentation. In conclusion, our results suggest that an altered Th response may be a consequence of inappropriate early activation events.

SUMMARY Neutrophils represent an important line of innate host defence against invading microorganisms and their functional detriment during HIV infection, including accelerated spontaneous cell death, has been shown to contribute to AIDS development. Neutrophils are susceptible to apoptosis via Fas and an interaction between Fas and FasL was suggested originally as a mechanism to explain constitutive neutrophil apoptosis. We have explored some intracellular pathways leading to PMN apoptosis from 28 HIV‐infected patients and 24 healthy volunteers. As previously reported, accelerated spontaneous apoptosis was observed in HIV+ patients, but this did not correlate with viral load. Furthermore, an increase in the level of spontaneous apoptosis was detected in neutrophils from HIV‐infected patients following inhibition of ERK, suggesting an impairment of this kinase pathway during the early stages of infection which may contribute to PMN dysfunction. An elevated susceptibility to undergo apoptosis was observed following cross‐linking of Fas, which correlated both with viral load and co‐expression of Fas/FasL surface molecules. Different mechanisms for spontaneous and Fas‐induced apoptosis are proposed which together contribute to the neutropenia and secondary infections observed during the progression to AIDS.

T cell response against HBV is vigorous in patients with acute hepatitis who clear the virus, whereas it is weak and narrowly focused in patients with chronic disease. We report that following incubation with HBcAg, a population of CD4+FoxP3+ cells expressing phenotypic markers of both natural and induced Tregs, can be antigen-induced from peripheral mononuclear cells. Conversely, naive and naturally immune subjects did not increase CD4+FoxP3+ Tregs following stimulation with HBcAg, supporting the idea that natural Tregs are able to respond specifically to HBV antigen. Furthermore, increased frequencies of antigen-induced CD4+FoxP3+IL-10+ Tregs correlated with viral load, suggesting that antigen-induced Tregs could contribute to an inadequate response against the virus, leading to chronic infection and support the view that specific natural Tregs may be implicated in host immune tolerance during HBV infection.

Human natural killer (NK) cells (CD56+ CD3-) represent crucial components of the innate immune system especially against viral infections and because their activation can modulate the outcome of the adaptive immune response. NKT cells (CD56+CD3+), a lymphocyte T population characterized by expression of surface markers of NK cells, are known to be abundant in the liver and their activation could be associated with hepatic injury. Using three-color flow cytometry to measure surface receptors and intracellular cytokines, we have explored early activation signals and cytokine production in NK and NKT cells within a group of hepatitis B vaccinated and non-vaccinated individuals. A specific increase of the CD56bright cell population, the activation receptor CD69 and IFN-gamma, was observed in NK cells following incubation with recombinant HBsAg in responders to vaccination. Comparable results were observed in NKT cells showing an increment of CD69, CD25, IL-2 and IFN-gamma expression in responder subjects. These parameters were statistically diminished in non-responder individuals (p<0.05) in both groups of cells. These results demonstrate a diminished activation of these cells in non-responders to the vaccine, suggesting that NK and NKT cells play an important role in the immune response following hepatitis B vaccination.

The immune system of HIV+ patients is chronically activated, which has been associated with a detrimental effect on both innate and acquired immunity during AIDS. We analyzed the expression and modulation of the triggering markers CD69 and CD16 in CD56+ cells from 18 asymptomatic HIV+ individuals and 8 AIDS patients, compared with 21 seronegative subjects. We observed a diminished PMA-induced CD16 downregulation in AIDS patients (p<0.01), associated with low numbers of CD4+ cells (p<0.02). Furthermore, an enhanced unstimulated expression of CD69 in asymptomatic HIV+ patients (p<0.05) was shown. AIDS patients could not efficiently upregulate PHA-dependent CD69 expression (p<0.05), which correlated with low CD4+ counts (p< 0.05). These abnormalities in CD16 and CD69 modulation were recorded in patients under highly active antiretroviral therapy (HAART). Our results demonstrate an altered modulation of two functionally relevant receptors in CD56+ cells from AIDS patients, contributing to our understanding of the immunopathogeny of NK cell dysfunction during disease progression.