Recognition of Self and Non-Self

The ability of the immune system to distinguish between 'self' and 'non-self' is fundamental to its function. This section explores how the body identifies foreign entities and why it doesn't attack its own cells.

Definition: An antigen is a molecule that induces an immune response in the body. Antigens can be proteins or glycoproteins.

Key points about self and non-self recognition:

1. All cell types, viruses, toxins, and organic materials have proteins or marker molecules on their surface that identify them.

2. The specific immune system can target different antigens and respond to them specifically.

3. Lymphocytes use the shape of molecules to identify non-self matter that needs to be destroyed.

4. The body produces millions of different lymphocytes capable of identifying various infections early in development. These remain in the body throughout life.

Highlight: The immune system's ability to recognize 'self' prevents it from attacking the body's own cells.

Protein markers, such as MHC proteins, play a crucial role in distinguishing native cells (self) from foreign cells (non-self). This mechanism ensures that the immune system only targets potential threats while leaving healthy body cells unharmed.

Vocabulary: MHC (Major Histocompatibility Complex) proteins are a group of genes that code for proteins found on the surface of cells that help the immune system recognize foreign substances.

Understanding this concept of self and non-self recognition is essential for A level Biology immunity Notes and forms the basis for comprehending more complex immune processes, including autoimmune disorders and transplant rejection.

Phagocytosis and White Blood Cells

Phagocytosis is a crucial process in the non-specific immune response, forming an important part of the body's defense against pathogens. This section delves into the types of white blood cells and the detailed steps of phagocytosis.

There are two main types of white blood cells:

1. Phagocytes: These cells ingest and destroy pathogens through phagocytosis before they can cause harm.
2. Lymphocytes: These are involved in immune responses.

Definition: Phagocytosis is the process by which cells engulf large particles, including pathogens.

The process of phagocytosis involves several steps:

1. Attraction: Chemical products of the pathogen attract the phagocyte along a concentration gradient.
2. Attachment: Receptors on the phagocyte's cell-surface membrane attach to chemicals on the pathogen's surface.
3. Engulfment: The phagocyte engulfs the pathogen, forming a phagosome.
4. Digestion: Lysosomes within the phagocyte release lysozymes into the phagosome, hydrolyzing the pathogen.
5. Absorption and Disposal: The hydrolysis products of the pathogen are absorbed by the phagocyte.

Highlight: Phagocytes can move out of blood vessels and into other tissues, allowing them to respond to infections throughout the body.

The final step in this process is crucial for the specific immune response:

6. Antigen Presentation: The phagocyte attaches the antigen to its surface in a complex called MHC (Major Histocompatibility Complex).

Vocabulary: MHC (Major Histocompatibility Complex) is a set of cell surface proteins essential for the acquired immune system to recognize foreign molecules.

This detailed understanding of phagocytosis is essential for A level Biology immunity notes and forms a foundation for comprehending more complex immune processes.