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Trichophyton
Immediate Hypersensitivty
vs.
Delayed-Type Hypersensitivity
(IH vs. DTH)
Trichophyton antigens exhibit both immediate hypersensitivity and delayed-type hypersensitivity skin tests. Immediate Hypersensitivity (IH) is associated with chronic cases of Trichophyton and a Th2-like response by the immune system. With these skin tests the reaction will occur with in minutes of exposing the skin to the pathogen. The reaction is portrayed as a wheal and flare at the site of exposure. The humoral or antibody sector of the immune system, specifically the immunoglobulin E or IgE and immunoglobulin G or IgG mediate the immune response within a few minutes (Woodfolk 2005 and Woodfolk et al. 2000). Once the antigen, mannan, is bound to IgE or IgG on a monocyte, the monocyte will degranulate to release pro-inflammatory effector cells such as histamine (Svegaard 1986). Svegaard found that IgG antibodies in 62% in patients with athlete’s foot (tinea pedis) and supported Woodfolk’s observation that these antibodies were constant in chronic cases, but only present briefly in acute cases. The importance of antibodies is still unknown in the immune response against Trichophyton because the pathogen is not completely cleared, but the antibodies are still present with high antigen loads at site of infection (Woodfolk).
Figure 4. Conidia of Trichophyton rubrum. Surrounding the fibrils and conidia in this image is the Trichophyton cell wall. One component of the cell wall is mannan, which aids in the digestion of the pathogen. Without an adequate cell-mediated response, the body is unable to eliminate the fungus completely.
Delayed-Type Hypersensitivity (DTH) is associated with the acute cases of Trichophyton and is caused by an immune system that has already been exposed to the antigen before, so the T cells already have seen the antigen. The activated macrophage from the innate immune response responds in the Th1 manner to the T helper cells. Th1 cells activate macrophages through IFN-gamma and aid in production of antibodies (Janeway et al. 2005). DTH reactions respond usually hours or days after exposure. What is interesting about Trichophyton is that it seems that DTH is only present briefly and then disappears after a few days. Afterward only wheals are present indicating an IH response (Ito 1963). Even with continual, systemic infection DTH is nonexistent in some patients and thus the patients cannot rid of the pathogen (Woodfolk). Although once either the Th1 or Th2 responses are dominating the response, in general for all diseases detected by the immune system, it is hard to shift to the other response. Which is just a mechanistic consequence of the immune system. In experiments with mice and using different purified Trichophyton allergen epitopes, the immune system produced distinct IH and DTH responses. In the instance of a DTH response, the cell-mediated immune response could clear infection while the IH still persisted (Woodfolk). The section called “Evasion of Immune Response Detection” will elaborate more on why there seems to be little to no cell-mediated immunity even though in an experimental setting it is able to clear the infection. In “Treatments and Future Research” will describe ways in which this portion of the adaptive immune response can be reborn.
Evasion of Immune System Detection
Prevention & Treatment and Future Research
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