HHIS221: HUMAN HISTOLOGY
Lesson 9 | Immune system and Lymphoid Organs
Adaptive immunity
● Acquired gradually by exposure to microorganisms,
Topic Outline:
● Immune System and Lymphoid Organs ● More specific
● Lymphocyte Origins/ Differentiation ● Develops more slowly and is based on antigen
presentation to lymphocytes – more accurate
● Responses are aimed at specific microbial invaders and
IMMUNE SYSTEM & LYMPHOID ORGANS
involve production of memory lymphocytes so that a
Immune System
similar response can be mounted very rapidly if that
● Provides defense or immunity against infectious agents
invader ever appears again
ranging from viruses to multicellular parasites
● Response involves B and T lymphocytes
● Consists of a large, diverse population of leukocytes
● Antigens – Usually proteins; that are recognized by
located within every tissue of the body and lymphoid
lymphocytes to elicit a specific immune response
organs interconnected only by the blood and lymphatic
against them (component of microorganisms)
circulation
● Antibodies – immunoglobulins produced by plasma
● Two fundamental lines of defense:
cells after a progenitor B cell is activated by a specific
1) innate immunity
antigen
2) adaptive immunity
Major Histocompatibility Complexes (MHC)
Innate immunity
● are cell surface glycoproteins whose primary function is
● represents the first line of defense to an intruding
to present peptide fragments for recognition by the
pathogen
appropriate T cells (lymphocytes)
● It is an antigen-independent (non-specific) defense
1) MHC Class I Molecules.- found on surfaces of all
mechanism that is used by the host immediately or within
nucleated cells bear fragments of their constituent
hours of encountering an antigen.
proteins
● including physical barriers such as the skin and mucous
2) MHC Class II Molecules - Only antigen-presenting
membranes of the gastrointestinal, respiratory, and
cells (APCs)
urogenital tracts that prevent infections or penetration of
3) Both of them have the common task of presenting
the host body
peptides to be recognized by T cells on the cell
● involves leukocytes (mainly granulocytes), and proteins
surface.
such as defensins, complement,lysozyme, and
Two forms of adaptive immune response
interferons; cytokines
1) Humoral immunity
● Hydrochloric acid (HCl)
● which antibodies are primarily responsible for the
● Defensins, short cationic polypeptides produced by
response
neutrophils and various epithelial cells that kill bacteria by
● B cell lymphocytes, a type of immune cell that
disrupting the cell walls.
makes antibodies after detecting a specific antigen,
● Lysozyme, an enzyme made by neutrophils and cells of
are principally responsible for this method
epithelial barriers, which hydrolyzes bacterial cell wall
2) Cell-mediated immunity
components, killing those cells.
● Mature T cells lymphocytes, macrophages, and
● Complement, a system of proteins in blood plasma,
the production of cytokines in response to an
mucus, and macrophages that react with bacterial
antigen are the main drivers of cell-mediated
surface components to aid removal of bacteria.
immunity.
● Interferons, paracrine factors from leukocytes and
virus-infected cells that signal NK cells to kill such cells
and adjacent cells to resist viral infection.
1
Lesson 9 | Immune system and Lymphoid Organs
Adaptive immunity
● Acquired gradually by exposure to microorganisms,
Topic Outline:
● Immune System and Lymphoid Organs ● More specific
● Lymphocyte Origins/ Differentiation ● Develops more slowly and is based on antigen
presentation to lymphocytes – more accurate
● Responses are aimed at specific microbial invaders and
IMMUNE SYSTEM & LYMPHOID ORGANS
involve production of memory lymphocytes so that a
Immune System
similar response can be mounted very rapidly if that
● Provides defense or immunity against infectious agents
invader ever appears again
ranging from viruses to multicellular parasites
● Response involves B and T lymphocytes
● Consists of a large, diverse population of leukocytes
● Antigens – Usually proteins; that are recognized by
located within every tissue of the body and lymphoid
lymphocytes to elicit a specific immune response
organs interconnected only by the blood and lymphatic
against them (component of microorganisms)
circulation
● Antibodies – immunoglobulins produced by plasma
● Two fundamental lines of defense:
cells after a progenitor B cell is activated by a specific
1) innate immunity
antigen
2) adaptive immunity
Major Histocompatibility Complexes (MHC)
Innate immunity
● are cell surface glycoproteins whose primary function is
● represents the first line of defense to an intruding
to present peptide fragments for recognition by the
pathogen
appropriate T cells (lymphocytes)
● It is an antigen-independent (non-specific) defense
1) MHC Class I Molecules.- found on surfaces of all
mechanism that is used by the host immediately or within
nucleated cells bear fragments of their constituent
hours of encountering an antigen.
proteins
● including physical barriers such as the skin and mucous
2) MHC Class II Molecules - Only antigen-presenting
membranes of the gastrointestinal, respiratory, and
cells (APCs)
urogenital tracts that prevent infections or penetration of
3) Both of them have the common task of presenting
the host body
peptides to be recognized by T cells on the cell
● involves leukocytes (mainly granulocytes), and proteins
surface.
such as defensins, complement,lysozyme, and
Two forms of adaptive immune response
interferons; cytokines
1) Humoral immunity
● Hydrochloric acid (HCl)
● which antibodies are primarily responsible for the
● Defensins, short cationic polypeptides produced by
response
neutrophils and various epithelial cells that kill bacteria by
● B cell lymphocytes, a type of immune cell that
disrupting the cell walls.
makes antibodies after detecting a specific antigen,
● Lysozyme, an enzyme made by neutrophils and cells of
are principally responsible for this method
epithelial barriers, which hydrolyzes bacterial cell wall
2) Cell-mediated immunity
components, killing those cells.
● Mature T cells lymphocytes, macrophages, and
● Complement, a system of proteins in blood plasma,
the production of cytokines in response to an
mucus, and macrophages that react with bacterial
antigen are the main drivers of cell-mediated
surface components to aid removal of bacteria.
immunity.
● Interferons, paracrine factors from leukocytes and
virus-infected cells that signal NK cells to kill such cells
and adjacent cells to resist viral infection.
1
