Immunity Lecture Notes

Cell Mediated Immunity

• Cell-mediated immunity primarily involves T cells.
• T cells are activated when they bind to a foreign antigen.
• Helper T cells (TTH) release cytokines, specifically interleukins, which act as messengers.
• Cytokines can:
  • Cause T cells to proliferate, increasing their numbers to combat the pathogen.
  • Activate cytotoxic T cells (TC), which kill cells.
• Cytotoxic T cells contain cytotoxins within depth patches.
• Upon activation, cytotoxic T cells release cytotoxins, inducing apoptosis (programmed cell death) in diseased or damaged cells, including cancer cells and virus-infected cells.
• Cell-mediated immunity involves T cells destroying damaged cells, whether they are cancerous or infected with a virus.

Phagocytosis

• Phagocytosis is the process by which cells "eat" other cells.
• Phagocytic cells, like macrophages, have arms to engulf bacterial cells.
• The phagocyte engulfs the bacterium through endocytosis, bringing it into the cell within a vesicle.
• This vesicle, formed by the plasma membrane, is called a phagosome.
• The hydrolitic enzymes inside lysosomes are released into the phagosome when the vesicles fuse, creating a phagolysosome.
• Hydrolytic enzymes break down the bacterial cell within the phagolysosome.
• After breakdown, contents can be exocytosed or processed further.
• Specialized proteins can take pieces of the digested bacteria (antigens) and present them on the cell surface.
• The antigen binds to a self protein (like a "goal post"), forming a self-non-self complex that alerts other immune cells to the presence of the antigen.
• This antigen presentation leads to a cell-mediated response involving T cells.

Clonal Selection Theory

• Clonal selection theory explains how B cells are selected to combat specific pathogens.
• B cells mature in lymphatic organs like lymph nodes.
• Each B cell has unique receptors (BCRs) on its surface, resembling antennae with specific binding sites.
• These unique shapes on the BCRs are called antigen-binding sites.
• Antigens are foreign bodies, such as those on the surface of viruses or bacterial cells, that elicit an immune response.
• Antigen Binding Site: Region of the B cell receptor that interacts with the antigen.
• When an antigen binds to a B cell receptor, it activates the B cell, making it experienced rather than naive.
• B cell activation leads to proliferation, increasing the number of B cells with the specific BCR.
• Proliferation enhances the clone of B cells that have the specific antigen binding site.
• These B2 clones can do something with the B cell receptor.
• Proliferated B cells differentiate into:
  • Plasma cells: produce and release large quantities of antibodies (Y-shaped proteins).
  • Memory cells: remain in the lymphatic system for long-term immunity.
• Memory cells respond quickly upon subsequent exposure to the same antigen, resulting in a much faster secondary immune response.