209 11-20-24

Antibody Use in Diagnostics and Therapy

• Antibodies bind highly specifically, making them useful for detecting pathogens, host cells, or molecules.
• Antibodies are also used therapeutically to inactivate toxins, inflammatory cytokines, and cancer cells.

ELISA (Enzyme-Linked Immunosorbent Assay)

• ELISA uses antibodies to detect pathogens and infections.
• The process involves coating wells with a specific antibody for a pathogen, then adding patient samples.
• If the pathogen antigen is present in the sample, it will bind to the antibody and the complex is detected by a secondary, enzyme-labeled antibody.
• The enzyme activity produces a colored product proportional to the amount of antibody.

Rapid Diagnostic Tests

• Rapid diagnostic tests use antibodies for quick pathogen detection.
• These tests often employ labeled antibodies (e.g., gold-labeled) bound to a solid phase.
• The presence (or absence) of bound antigen can be detected visually.
• They are helpful in clinical settings for prompt diagnoses.

T Cell Effector Functions

• Cytotoxic T cells (CD8+) kill infected cells by releasing cytotoxic toxins.
• Helper T cells (CD4+) interact with other immune cells to regulate the immune response.
• TH1 cells aid in cell-mediated responses against intracellular pathogens.
• TH2 cells help in antibody-mediated responses.
• TH17 cells aid in the response against extracellular pathogens.

T Cell Development and Function

• T cells develop in the thymus and express unique, specific antigen receptors.
• These receptors have unique antigen specificities during development.
• Antigen recognition activates T cells, which then differentiate into effector or memory cells.
• Mature T cells can recognize antigens only after processing and presentation by antigen-presenting cells.
• T cells play a crucial role in the adaptive immune response to pathogens.
• T cells primarily recognize pathogen-derived peptides bound to MHC molecules. The peptides (fragments) are presented by antigen-presenting cells (APCs) on their surface.

T Cell Activation

• T cell activation requires the TCR to bind to an antigen presented on MHC molecules and involves co-receptor interactions.
• MHC I is recognized by CD8+ cytotoxic T cells, while MHC II is recognized by CD8+ helper T cells.

T Cell Activation and Killing of Infected Cells

• Activated CD8+ cytotoxic T cells kill infected cells by releasing cytotoxic enzymes that induce apoptotic pathways.
• This process is comparable to mechanisms used by NK cells (natural killer cells).
• Antigen (virus) is brought into the cell, where it is processed, triggering the T-cell activation process.

CD4 T Cell Subsets

• Various CD4+ T helper cell subsets exist, each with distinct functions and cytokine profiles.
• TH1 cells produce interferon-gamma and help eradicate intracellular bacteria.
• TH2 cells produce cytokines promoting B cell activation for antibody production against extracellular bacteria.
• TH17 cells produce cytokines to fight extracellular pathogens and inflammation.

T Helper Cell Functions in Immune Response

• TH1 helper cells stimulate phagocytic cells, aiding in improving pathogen killing.
• TH1 helper cells also assist cytotoxic T cell activation.
• TH2 helper cells help B cells proliferate and differentiate, leading to antibody production.