Topic: Humoral and cell mediated immunity
Question:Describe the mechanism of cell mediated immune response. Add a note on its applications, detection methods, and name the immunodeficiency diseases associated with defect in cell mediated immunity.
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What is Cell-Mediated Immunity?
– It refers to immune responses mediated by T lymphocytes (T cells) and does not involve antibodies.
– It is required to eliminate intracellular pathogens like viruses, bacteria, and protozoa from infected cells.
– It also eliminates cancer cells and transplanted tissues.
Mechanism of Cell-Mediated Immune Response:
1. Antigen-presenting cells (APCs) like dendritic cells phagocytose the pathogen and digest it into small peptide fragments.
2. These antigenic peptides are presented on MHC class I or class II molecules on the surface of APCs.
3. CD4+ helper T cells recognize antigen-MHC class II complexes via their T cell receptor (TCR). This activates them.
4. Activated CD4+ cells release cytokines like IFN-gamma, IL-2, TNF-beta that further stimulate phagocytes and CD8+ T cells.
5. Cytokines help recruit and activate more macrophages which phagocytose and kill microbes.
6. CD8+ cytotoxic T cells recognize infected cells displaying antigen-MHC class I complexes via their TCRs.
7. Activated CD8+ T cells kill infected cells directly by releasing perforin, granzymes and granulysin.
8. Memory T cells are generated that persist after infection to provide long-term immunity.
Applications of Cell-Mediated Immunity Testing:
– Assessing immune system function in immunocompromised patients.
– Diagnosing defects in cell-mediated immunity.
– Monitoring HIV disease progression and treatment response.
– Testing for latent tuberculosis.
Detection Methods:
– Skin delayed-type hypersensitivity test.
– Quantification of T cell subsets like CD4+, CD8+ cells.
– In vitro lymphocyte proliferation assay.
Associated Immunodeficiencies:
– Severe combined immunodeficiency (SCID)
– DiGeorge syndrome
– Wiskott-Aldrich syndrome
– Chronic granulomatous disease
– HIV/AIDS
