Chapter 14: Genetics, Altered Immune Responses, and Transplantation
Genetic disorders can be categorized into autosomal dominant, autosomal recessive, or sex-
linked (X-linked) recessive disorders.
o Autosomal dominant disorders are caused by a mutation of a single gene pair
(heterozygous) on a chromosome.
o Autosomal recessive disorders are caused by a mutation in two gene pairs
(homozygous) on a chromosome.
o X-linked recessive disorders are caused by a mutation on the X chromosome.
The different types of genetic testing include direct testing, linkage testing, biochemical testing,
Gene therapy is an experimental technique used to replace or repair defective or missing genes
with normal genes.
Stem cells are cells in the body that have the ability to differentiate into other cells. Stem cells
can be divided into two types: embryonic and adult.
ALTERED IMMUNE RESPONSES
Immunity is a state of responsiveness to foreign substances such as microorganisms and tumor
proteins. Immune responses serve three functions: defense, homeostasis, and surveillance.
Immunity is classified as innate (natural) or acquired. Acquired immunity is the development of
immunity, either active or passive.
The immune response involves complex interactions of T cells, B cells, monocytes, and
neutrophils. These interactions depend on cytokines (soluble factors secreted by WBCs and a
variety of other cells in the body) that act as messengers between the cell types.
Humoral immunity consists of antibody-mediated immunity. In contrast, immune responses
initiated through specific antigen recognition by T cells are termed cell-mediated immunity.
Both humoral and cell-mediated immunity are needed to remain healthy. Immunocompetence exists when the body’s immune system can identify and inactivate or
destroy foreign substances.
A hypersensitivity reaction occurs when the immune response is overreactive against foreign
antigens or fails to maintain self-tolerance. This results in tissue damage.
Although an alteration of the immune system may be manifested in many ways, allergies or type
I hypersensitivity reactions are seen most frequently.
o Common allergic reactions include anaphylaxis and atopic reactions.
o Allergic rhinitis, atopic dermatitis, urticaria, and angioedema are common type I
After an allergic disorder is diagnosed, the therapeutic treatment is aimed at reducing exposure
to the offending allergen, treating the symptoms, and if necessary, desensitizing the person
Anaphylactic reactions occur suddenly in hypersensitive patients after exposure to the