Kåre Kemp

T-cell response in human leishmaniasis

In the present communication we provide evidence for the existence of a Th1/Th2 dichotomy in the T-cell response to Leishmania antigens in human leishmaniasis. Our data suggest that the pattern of IL-4 and IFN-gamma response is polarised in these patients. Lymphocytes from individuals recovered from cutaneous leishmaniasis (CL) responded by IFN-gamma production following stimulation with Leishmania antigens whereas cells from patients recovered from visceral leishmaniasis (VL) showed a mixed pattern of IFN-gamma and IL-4 responses. The cells producing these cytokines were predominantly CD4+. Furthermore, IL-10 plays an important role in the development of post kala azar dermal leishmaniasis (PKDL) from VL. The balance between the parasitic-specific T-cell response plays an important regulatory role in determining the outcome of Leishmania infections in humans.

Chalcones from Chinese liquorice inhibit proliferation of T cells and production of cytokines.

Licochalcone A (LicA), an oxygenated chalcone, has been shown to inhibit the growth of both parasites and bacteria. In this study, we investigated the effect of LicA and four synthetic analogues on the activity of human peripheral blood mononuclear cell proliferation and cytokine production. Four out of five chalcones tested inhibited the proliferation of lymphocytes measured by thymidine incorporation and by flow cytometry. The production of pro- and anti-inflammatory cytokines from monocytes and T cells was also inhibited by four of five chalcones. Furthermore, intracellular detection of cytokines revealed that the chalcones inhibited the production rather than the release of the cytokines. Taken together, these results indicate that LicA and some analogues may have immunomodulatory effects, and may thus be candidates not only as anti-microbial agents, but also for the treatment of other types of diseases.

Leishmania-specific T cells expressing interferon-gamma (IFN-γ) and IL-10 upon activation are expanded in individuals cured of visceral leishmaniasis

Peripheral blood mononuclear cells (PBMC) from patients who have recovered from visceral leishmaniasis often respond to Leishmania antigens in vitro by production of both IL‐4, IFN‐γ and IL‐10. In order to establish the cellular sources of these cytokines, we activated cells from individuals with a history of visceral leishmaniasis with Leishmania antigen for 6 days in culture, and identified cytokine production at the single‐cell level by flow cytometry. The cytokines were only found in CD3+ cells and among these mainly within the CD4+ subset. The percentage of cytokine‐producing cells was compared in Leishmania‐activated PBMC cultures from the previous patients and from individuals living in a village where leishmaniasis does not occur. The percentage of IL‐10‐ and IFN‐γ‐containing cells was significantly higher in the previous patients than in the controls, indicating that Leishmania‐specific T cells producing IL‐10 and/or IFN‐γ had been expanded as a result of the infection. The cytokine‐producing cells in the previous patients could be divided into three types: (i) cells producing IFN‐γ only; (ii) cells producing IL‐4 only; and (iii) cells producing IFN‐γ and IL‐10 simultaneously. The first and second group of cells can be described as Th1‐ and Th2‐type cells, respectively. The third group could be a regulatory subset of T cells important for maintaining a balance between Th1‐ and Th2‐type cells in these individuals.

Pneumococcal Infections in Humans Are Associated with Increased Apoptosis and Trafficking of Type 1 Cytokine-Producing T Cells

ABSTRACT Streptococcus pneumoniae infections are associated with considerable morbidity and mortality throughout the world. The immunopathology is characterized by an intense inflammatory reaction, including a strong acute-phase response and increased numbers of neutrophils in the circulation. However, little is known regarding the T-cell response during in vivo infections in humans. The purpose of this study was to test the hypothesis that activated T cells producing type 1 cytokines were engaged in the host response to pneumococcal infections. The phenotype and function of T cells were studied in 22 patients at admission to a department of infectious diseases and after antibiotic treatment for 1 week compared with an age-matched, healthy control group. Pneumococcal infections induced lymphopenia in the circulation due to the disappearance of activated T lymphocytes with a type 1 cytokine profile. In contrast, the numbers of naive T cells and interleukin-4-producing T cells did not change. Activated type 1 cytokine-producing cells reappeared in the circulation in relation to the treatment and clinical improvement. The underlying mechanisms during infection may include sequestration in the peripheral tissues and/or apoptosis. In fact, increased activation-induced apoptosis in the remaining peripheral lymphocytes and elevated levels of soluble Fas ligand were detected at admission to the hospital. In conclusion, these data suggest that activated T lymphocytes with a type 1 cytokine profile are highly engaged in the in vivo immune response to S. pneumoniae.

Perturbation and proinflammatory type activation of Vδ1+ γδ T cells in African children with Plasmodium falciparum malaria

ABSTRACT γδ T cells have variously been implicated in the protection against, and the pathogenesis of, malaria, but few studies have examined the γδ T-cell response to malaria in African children, who suffer the large majority of malaria-associated morbidity and mortality. This is unfortunate, since available data suggest that simple extrapolation of conclusions drawn from studies of nonimmune adults ex vivo and in vitro is not always possible. Here we show that both the frequencies and the absolute numbers of γδ T cells are transiently increased following treatment of Plasmodium falciparum malaria in Ghanaian children and they can constitute 30 to 50% of all T cells shortly after initiation of antimalarial chemotherapy. The bulk of the γδ T cells involved in this perturbation expressed Vδ1 and had a highly activated phenotype. Analysis of the T-cell receptors (TCR) of the Vδ1+ cell population at the peak of their increase showed that all expressed Vγ chains were used, and CDR3 length polymorphism indicated that the expanded Vδ1 population was highly polyclonal. A very high proportion of the Vδ1+ T cells produced gamma interferon, while fewer Vδ1+ cells than the average proportion of all CD3+ cells produced tumor necrosis factor alpha. No interleukin 10 production was detected among TCR-γδ+cells in general or Vδ1+ cells in particular. Taken together, our data point to an immunoregulatory role of the expanded Vδ1+ T-cell population in this group of semi-immuneP. falciparum malaria patients.

Cytokine production and apoptosis among T cells from patients under treatment for Plasmodium falciparum malaria.

Available evidence suggests that Plasmodium falciparum malaria causes activation and reallocation of T cells, and that these in vivo primed cells re‐emerge into the periphery following drug therapy. Here we have examined the cytokine production capacity and susceptibility to programmed cell death of peripheral T cells during and after the period of antimalarial treatment. A high proportion of peripheral CD3+ cells had an activated phenotype at and shortly after time of admission (day 0) and initiation of therapy. This activation peaked around day 2, and at this time‐point peripheral T cells from the patients could be induced to produce cytokines at conditions of limited cytokine response in cells from healthy control donors. Activated CD8hi and TCR‐γδ+ cells were the primary IFN‐γ producers, whereas CD4+ cells constituted an important source of TNF‐α. The proportion of apoptotic T cells was elevated at admission and peaked 2 days later, while susceptibility to activation‐induced cell death in vitro remained increased for at least 1 week after admission. Taken together, the data are consistent with the concept of malaria‐induced reallocation of activated T cells to sites of inflammation, followed by their release back into the peripheral blood where they undergo apoptotic death to re‐establish immunological homeostasis as inflammation subsides. However, the high proportion of pre‐apoptotic cells from the time of admission suggests that apoptosis also contributes to the low frequency and number of T cells in the peripheral circulation during active disease.

What Is the Cause of Lymphopenia in Malaria

Two recent reports conclude that Fas-induced apoptosis plays an important role in the lymphopenia of Plasmodium falciparum malaria in humans (5) and in Plasmodium coatneyi-infected macaques (6). In both studies, the authors base their conclusion on concomitant findings of increased levels of soluble Fas ligand in serum and lymphopenia. An important element in their arguments is the finding of spontaneous ex vivo T-cell apoptosis in P. falciparum patients from Senegal (1, 7). However, to our knowledge no other reports exist supporting the hypothesis that high levels of apoptotic cells in the peripheral blood are a general feature of P. falciparum malaria. We have never been able to detect significant increases in the proportion of peripheral T cells showing evidence of apoptosis in several studies of many malaria patients in Ghana, except once in a moribund cerebral malaria patient (our unpublished data). Indeed, Matsumoto et al. could detect apoptotic peripheral blood mononuclear cells (not necessarily T cells) in moribund animals only (6), in line with our findings but at variance with the Senegalese data where apoptotic cells were readily detected even in asymptomatic parasite carriers (7). Lymphopenia is a well-established feature of P. falciparum malaria but is replaced by lymphocytosis in a matter of a few days after initiation of drug therapy, before gradually normalizing over the next couple of weeks (4). How this can occur if the lymphopenia is the result of widespread apoptosis is difficult to imagine. Rather, we have proposed that the initial lymphopenia reflects disease-induced reallocation of T cells to sites of inflammation (2), followed by reemergence of such cells upon cure (4). Although apoptosis appears not to be involved in these changes, it can be speculated that the eventual return to predisease homeostasis is mediated by apoptosis of excess “battle-worn” T cells (Fig. ​(Fig.1).1). Whether such postmalaria apoptosis occurs remains uncertain, let alone whether it is detectable in the peripheral circulation and is mediated through Fas. Although the papers by Kern et al. (5) and Matsumoto et al. (6) provide evidence of both lymphopenia and increases in soluble Fas ligand, both fail to demonstrate any evidence that one is the consequence of the other. Until such evidence becomes available, we feel that reallocation/reemergence remains the most plausible explanation of the observed lymphopenia in malaria. FIG. 1 Schematic diagram of perturbations in numbers of peripheral T cells following Plasmodium infection. This hypothesis is supported by a number of independent studies, most recently by an investigation of peripheral and splenic cellular changes in P. chabaudi-infected mice (3).

Interferon-gamma production by human T cells and natural killer cells in vitro in response to antigens from the two intracellular pathogens Mycobacterium tuberculosis and Leishmania major.

Acquired resistance to both mycobacteria and Leishmania is primarily mediated by interferon‐γ (IFN‐γ), which triggers mechanisms leading to the death of the microorganism in macrophages. In this study, cell activation and IFN‐γ production was investigated in human peripheral blood mononuclear cells (PBMC) from individuals previously sensitized to tuberculin and without known exposure to Leishmania parasites. Immune staining for intracellular IFN‐γ and surface markers allowed flow cytometric identification of the cellular sources of IFN‐γ in cell cultures incubated with purified protein derivative of tuberculin (PPD) and Leishmania antigens. It was found that IFN‐γ was produced in response to both PPD and Leishmania stimulant by T cells in the cultures. Activation of IFN‐γ producing natural killer (NK) cells was demonstrated only in some cultures, and only with concomitant T cell activation.

West African donors have high percentages of activated cytokine producing T cells that are prone to apoptosis

Persistent immune activation has been suggested to affect the subset composition and activation status of peripheral blood cells. In this study we have compared peripheral blood mononuclear cells (PBMC) from a group of Ghanaians living in an area with high prevalence of malaria, mycobacteria, EBV and helmintic infections to a group of European counterparts. Our hypothesis was that persistent challenge with microorganisms is associated with increased production of cytokines and increased susceptibility of periphery cells to undergo apoptosis. We observed an increased frequency of activated T cells and a higher frequency of IL‐4‐ but not IFN‐γ‐producing cells in the periphery of the Ghanaians. The IL‐4 was produced mainly by CD4+ cells, in contrast to IFN‐γ which was produced equally by CD4+, CD8+ and TCR‐γδ+ cells. The frequencies of cytokine‐producing cells were highly correlated to the frequencies of activated cells. Finally, cells from Ghanaians were more susceptible to activation‐induced apoptosis. These results may explain why some epidemic diseases seem to have a different mode of transmission in Africa compared to the western world, and may thus be of importance when vaccine strategies are considered in Africa.

Acute P. falciparum malaria induces a loss of CD28- T IFN-γ producing cells

P. falciparum malaria is associated with increased activation among peripheral lymphocytes. In the present study, we investigated markers of susceptibility to apoptosis and expression of IFN‐γ and IL‐4 by CD28−and CD28+T cells in West African children with acute P. falciparum malaria. The study showed increased susceptibility to apoptosis and cytokine production among T lymphocytes during acute malaria but also that T cells, in particular IFN‐γ producing CD28−T cells, were substantially reduced. These results are in line with previous studies suggesting that certain T cell subsets are sequestered away from the peripheral blood during P. falciparum malaria.