adaptive immunity

Zika Virus Transmission and Immune Response

Transmission: The Zika virus is primarily transmitted by the Aedes aegypti mosquito.
As the mosquito feeds, it injects the virus into the bloodstream.

Antibodies: Y-shaped proteins produced by B cells that can surround viral particles.
- Function: Prevent viruses from infecting cells by blocking their ability to attach to cell receptors.
Viral Replication Steps:
1. Virus attaches to cell receptors.
2. Protective antibodies block this attachment, preventing the virus from entering the cell and replicating.
Immune System Overview:
- Discussion on the transition from the innate to the adaptive immune system.
- Focus on the humoral immune response, which produces antibodies.

Humoral Immune System: Works alongside the innate immune system.
- Antibodies can activate components of the innate immune response, such as phagocytosis.
Primary Immune Organ: Bone marrow is crucial for the production of blood cells, including B cells.

B Cells:
- Origin: Produced and mature in the bone marrow.
- Function: Activated by antigens to produce plasma cells and memory cells.
Structure of Antibodies:
- Comprising four polypeptide chains: two heavy chains and two light chains.
- Divided into two regions:
  - Variable region: Recognizes and binds to unique epitopes on antigens.
  - FC region: Constant across antibody classes and binds to receptors on host cells.

Antigens: Large foreign substances that trigger an immune response.
Epitopes: Smaller, specific parts of an antigen recognized by antibodies.
- Example: A bacterial cell as an antigen consists of many epitopes.

Neutralization: Antibodies bind to viruses or toxins, preventing them from interacting with cells.
Cross-linking: Antibodies can bind multiple antigens, facilitating phagocytosis.
Natural Killer Cells Role: Antibodies can mark infected cells for destruction by natural killer cells through FC receptor recognition.
Opsonization: Antibodies coat pathogens, enhancing recognition by phagocytes.
Complement Activation: Antibody-bound targets activate the complement system, leading to opsonization and cell lysis.
Prevention of Motility: Antibodies can bind flagella or pili, inhibiting movement and attachment.

IgM:
- First antibody produced in response to an antigen; good at cross-linking and activating complement.
IgG:
- Most abundant in blood and tissues; facilitates phagocytosis and activates complement.
IgA:
- Most abundant in mucosal areas; important for immune defense at mucosal surfaces.
IgE:
- Involved in allergic reactions and responses to parasitic infections; binds to mast cells and basophils.

B Cell Activation Process:
1. B cells recognize and bind to an antigen leading to internalization.
2. Processed antigens are presented on Major Histocompatibility Complex (MHC) for T cell recognition.
3. T-helper cells bind to B cells, providing the second activation signal via cytokines, prompting B cell differentiation into plasma cells.
T-independent Antigens: Some antigens can directly activate B cells without T cell assistance, often leading to a limited immune response.

Clonal Selection: B cells recognizing antigens are selected for proliferation.
Expansion: The selected B cells differentiate into plasma cells (producing antibodies) and memory B cells (for future responses).

First Exposure: Initial exposure results in IgM response, followed by IgG production.
Memory Cells: Cells that survive after the first exposure to facilitate rapid response upon subsequent exposures.
Vaccination Principle: Vaccines induce the formation of memory B cells and T cells, allowing for quicker and more effective responses to pathogens like the Zika virus upon re-exposure.