It is well established that the balance between functionally distinct regulatory CD4+ T cells plays a major role in the development of immunity and/or pathogenesis to many different infections. In spite of the importance of Th lineage commitment in disease, the critical questions how the balance between Th1 and Th2 cells is regulated is largely unresolved. This thesis describes work aimed at assessing CD4+ T cell heterogeneity and how this is regulated in humans naturally primed to P. falciparum malaria or vaccinated with tetanus toxoid or BCG.
Different types of antigens have been implicated to be of importance in the polarization of Th1 or Th2 cells. To investigate this, we stimulated peripheral blood mononuclear cells (PBMC) with tetanus toxoid (TT) and the mycobacterial antigen, purified protein derivative (PPD) in vitro and determined the number of IFN-g (Th1 cytokine) and IL-4 (Th2 cytokine) producing cells using the ELISPOT assay. PPD preferentially induced IFN-g and very few IL-4 producing cells, while TT- induced both IL-4 and IFN-g. These differences probably reflect the different types of immune responses the two antigens induce, mycobacteria preferentially a cell-mediated Th1 type of immunity, while immunity to tetanus is an antibody-dependent, Th2 type of response.
To investigate the role of Th1 and Th2 cells in the regulation of anti-malarial IgE in individuals living in P.falciparum endemic areas, the number of IL-4 and IFN-g producing cells was correlated to the plasma anti-malarial IgE levels. A negative correlation between the number of IFN-g producing cells and anti-P.falciparum IgE was found. For IL-4 there was a weak positive correlation with anti-malarial IgE levels, suggesting that other cells than T cells can produce IL-4. The anti-malarial IgE levels correlated significantly with an increased ratio of IL-4/IFN-g producing cells. These data suggest a regulatory role for IL-4 in the induction of anti-P.falciparum IgE antibodies.
When PBMC from two groups of individuals naturally exposed to P.falciparum, living in two different parts of Africa (Burkina Faso and Tanzania), were stimulated in vitro with P.falciparum antigens, no malaria-specific IL-4 producing cells were detected. The levels of IgE were lower in the Burkina individuals as compared to the Tanzania ones. This might reflect differences in malaria exposure or genetic (ethnic) differences between the two study groups.
To study the influence of genetic and/or environmental factors on the development and shaping of the human peripheral T cell repertoire, the T cell receptor (TCR) Vb usage in ten adult monozygous (Mz) and nine dizygous (Dz) twin pairs living in a P.falciparum endemic area in The Gambia was studied. The results revealed that the frequencies of cells expressing particular TCR Vb genes were not influenced by the parasitaemia, indicating that malaria exposure is not a dominating factor in shaping the peripheral TCR repertoire in humans. The mean within-pair difference was significantly lower for the Mz than for the Dz pairs. The mean within-pair difference for a group of MHC-class II identical twin pairs was significantly higher than for the Mz group but similar to that of the Dz as a whole. These data indicate that genetic factors other than MHC class II genes (i.e non-MHC) influence the shaping of the peripheral TCR Vb repertoire in humans.
To study whether or not IgE-containing malaria sera have the capacity to induce IL-4 in human basophils, IgE containing sera from malaria immune donors were added to tissue culture plates coated with anti-human IgE antibodies. IgE-anti-IgE complexes induced IL-4 in basophils. Serum depleted of IgE induced significantly less IL-4. These data show that malaria IgE can induce IL-4 production in cells of basophil origin that can subsequently amplify Th2 type of responses.
Taken together, our data show the existence of functionally distinct T cells in individuals naturally primed to P.falciparum or vaccinated with TT or BCG.
Stockholm: Stockholm University , 1999. , 59 p.