Genetics of Immunity 1 - Human Immune System
Immune system protects organisms from foreign invaders.
Foreign versus self
•To protect the body from harmful organisms, the immune system identifies foreign molecules as “nonself” and destroys those cells.
•Molecules recognized by the immune system are called antigens. Antigens are usually protein fragments or carbohydrates.
•During development, the immune system removes components that recognize “self”.
•Immune response to one’s own body is called autoimmunity.
•Rh factor or rhesus factor is another blood group affecting cell surface molecules.
•Three genes affect this phenotype.
Rh+ produces Rh factor on RBC
Rh- no Rh factor on RBC
Rh incompatibility occurs when an Rh- mother has an Rh+ child.
II. Human leukocyte antigens (HLA)
•HLA proteins are produced by major histocompatibility complex (MHC) class I and II genes.
•Link sugars to form branched glycoproteins on cell surface of white blood cells.
•HLA glycoproteins can recognize bacterial and viral proteins, marking them for immune system to target, a process called antigen processing.
Antigen Presenting Cells
Several genes with multiple alleles determine an HLA type.
Genetic diversity at HLA genes is large.
•Only 1 in 10,000 unrelated people will share an HLA type by chance at the six major HLA genes.
•Matching at least 4 major HLA genes is needed for most transplants to succeed.
HLA genes account for about 50% of the genetic impact on immunity.
III. Components of the immune system
Lymphatic system of duct and nodes
Lymph, fluid filling lymph ducts
1. Organs involved in production or maturation of immune cells
2. Immune system cells
Many cells types contribute to immune response
Types of immune cells
Levels of immune protection
Mucous membranes and secretions
3. Infection fighting chemicals in tears and saliva
Flushing effect of tears, saliva, urination, and diarrhea
Nonspecific innate defense
• Complement system
– tumor necrosis factor
4. Inflammatory response
Inflammation: an innate defense system
Complement system kills bacteria
Specific, Adaptive Immunity
Response time is in days.
Diversity many different pathogens recognized
Specificity distinguishes particular molecules
Memory responds faster with subsequent exposure
Primary immune response is reaction to first exposure.
Secondary immune response is reaction to exposure using “memory” of first response.
Specific, Adaptive Immunity
5. Two types of response:
Humoral immune response
B cells, antibodies, memory cells
Cellular immune response:
T cells, cytokines, memory cells
Activated B cells produce antibodies and memory cells
Function of Antibodies
Types of antibodies or immunoglobins (Ig)
•There are numerous but limited antibody genes in the human genome.
•During early development of B cells, sections of the antibody genes are rearranged along their chromosome.
•Rearrangement of Ig genes creates new versions of the antibody proteins.
•By shuffling 200 genes, over 100 trillion different antibodies can be produced.
•A single stimulated B cell produces the same antibody combinations.