Bela Chauhan

CELL-MEDIATED IMMUNITY IN ALLERGIC BRONCHOPULMONARY ASPERGILLOSIS

Allergic bronchopulmonary aspergillosis (ABPA) is a hypersensitivity lung disease mediated by an allergic late-phase inflammatory response to Aspergillus fumigatus antigens characterized by markedly elevated allergen specific and total immunoglobulin E (IgE) levels and eosinophilia, and manifested by wheezing, pulmonary infiltrates, and pulmonary bronchiectasis and fibrosis. ABPA afflicts only a small percentage of susceptible atopic individuals with either asthma or cystic fibrosis (CF). ABPA is unique in that it is caused by A. fumigatus, a living fungus growing within the mucosal lumen of the bronchi that releases a multitude of proteins whose biologic function alters the host immune responses in addition to being immunogenic. Elucidation of the immunopathogenesis of ABPA has provided valuable information related to allergen-induced chronic asthma. More recently, immunogenetic studies have further contributed to the understanding of the immunopathogenesis of why certain individuals are susceptible to develop ABPA. Immunologic responses to Aspergillus, as well as to other microorganisms, may be categorized as either T helper (Th)1 or Th2 CD4+ T-cell responses. 61,110,128 Th1 CD4+ T-cell cytokines, such as interferon gamma (IFN-γ), interleukin 2 (IL-2), and tumor necrosis factor (TNF)-β, enhance cytotoxic and macrophage activity (e.g., cellular immunity), whereas Th2 CD4+ T-cell cytokines, such as IL-4, IL-5, IL-10, and IL-13, promote antibody synthesis (e.g., humoral antibody immunity) (Table 1). It is hypothesized that protective host immunity to A. fumigatus is a Th1 CD4+ T-cell response, whereas a Th2 CD4+ T-cell humoral response found in ABPA is nonprotective and leads to a hypersensitivity pulmonary lung disease.

T-cell receptor bias in patients with allergic bronchopulmonary aspergillosis.

CD4(+) Th2 helper cell mediated immune responses have been shown to play a crucial role in the pathogenesis of ABPA. HLA and TCR are the candidate genes, which can influence the specificity of these responses. We have previously established a strong association of HLA DR2/5 in ABPA susceptibility. The study was designed to determine whether allergen specific T cell express a limited usage of T cell receptor (TCR) Vbeta gene repertoire in ABPA and to find an association of susceptible HLA-DR determinants with the identified TCR gene segments. TCR Vbeta typing was performed on antigen specific T cell lines from 14 ABPA and 12 nonABPA patients. The majority of ABPA patients (86%) expressed allergen specific T cells with Vbeta13 genes indicating its role in susceptibility, whereas in nonABPA controls, Vbeta1 genes T cell repertoires were predominantly expressed. The unrestricted pattern of Vbeta gene amplification seen before antigen stimulation suggests an oligoclonal expansion of a specific T cell population in response to the allergen Asp f 1 in ABPA and nonABPA patients. The increased usage of Vbeta13 in ABPA and Vbeta1 in nonABPA indicates their importance in susceptibility and resistance, respectively.