Browsing by Author "Larbi, John Asiedu"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Anti-Filarial T-cell Responses in Onchocerciasis: Protective responses to recombinant Onchocerca volvulus antigens and regulatory mechanism
    (2005) Larbi, John Asiedu
    Onchocerciasis or River blindness is of high prevalence in tropical Africa, however current control methods, cannot stop transmission completely. Thus complementary approaches including the role of immune mechanisms to control have been advocated. The presence of putative immune individuals and evidence from animal models suggest the existence of immunity to onchocerciasis and that a mixed Thl/Th2 may be involved. To elucidate protective human immune responses, whole blood of onchocerciasis patients were stimulated with 17 O. volvulus recombinant antigens and the cytokine profiles elicited were assessed. Stimulation with these antigens induced moderate to high levels of cell proliferation and the production of IFN-γ, IL-5, IL-13 and IL-b. Interferon-γ production was observed to be significantly higher in cultures stimulated with the recombinant antigens OvALD, RAL-2 and ASP-1. These antigens also showed enhanced production of IL-S (P< 0.05). Only ASP-1 induced significant production of IL-13 (P=0.002). Thus, OvALD, RAL-2 and ASP-i proved potent in inducing a mixed Th1 /Th2 cytokine profile, and could be further investigated for vaccine development. The phenomenon of peripheral tolerance as observed in generalized onchocerciasis, involves different mechanisms. T regulatory-1 (Tr1) cells, a subset of CD4+ T cells, are implicated in suppressor functions in vitro and in vivo. Characterized by the predominant production of IL-10 and/or TGF-3, Tr1 cells have mainly been generated experimentally in an IL- 10-rich environment and have not been characterized in infectious diseases. In this study, it is shown that in the chronic helminth infection of onchocerciasis, T cells can be obtained which bear characteristics of Tr1 cells, producing substantial amounts of IL- 10, variable amounts of IL-5, and some IFN-γ but no IL-2 or IL-4. In contrast to Thl and Th2 clones, these cells display elevated amounts of CTLA-4 after stimulation and are able to inhibit other T cells in coculture. The effect of T cells with a regulatory profile on IgG4 production was investigated using generated T cell clones (TCC) with two different cytokine profiles co-cultured with purified CD19+ B cells. The present study showed that in T-B cell co-culture, IL- 10, if induced by the TCC or added to the system, down-regulated the immune response by inducing IgG4 secretion. The correlation between IgG4 and IL-l0 (r2 = 0.352) indicates that IL-b is an important but not the only factor for IgG4 induction. This establishes a direct implication of IL-I 0 in humoral hyporesponsiveness; especially where the T-B cell interplay determines the subsequent immune response.
  • Thumbnail Image
    Item
    Studies on intestinal parasitic infections in school children in Kumasi
    (1998-07-29) Larbi, John Asiedu
    Intestinal helminthic infections are one of the world’s most common infections contributing directly to malnutrition, anaemia and low academic achievement in school children. Data on prevalence and distribution of helminthic infections are however scanty in Ghana. The present study, therefore, sought to determine the prevalence and distribution of helminthic infections among primary school children in Kumasi and also show how certain habits and practices may contribute significantly to levels of infestation. Stool samples from 3970 randomly selected primary school children were examined using the formol-ether concentration technique. Factual information on each child was also obtained using pretested questionnaires. The survey showed that intestinal helminth infection is prevalent (38.7%) among the school children with Ascariasis being the highest in prevalence (16.1%) followed by Hookworm infection and trichuriasis. Ascariasis was also of highest prevalence in schools in the southwestern, northwestern and northeastern parts of Kumasi whilst hookworm infection was highest in the southeastern part of Kumasi. Generally, children from public schools showed higher prevalence than their counterparts from private schools, however, no significant differences (P 0.05) were recorded with respect to prevalence by age and sex. Children who did not usually wash their hands before meals, after play and after defaecation, those who do not use dewormers and those who regularly eat Street foods showed higher levels of infection and were also more exposed to multiple worm infestations. A combination of hand washing and regular use of dewormers significantly affected levels of worm infestation. The implications of these observations are discussed. This situation calls for increased health education activities in schools and the need for periodic deworming.