Lecture 3 Acquired Immunity 794-798, 800
• Acquired immune responses are antigen-specific responses in which the body recognizes a
particular foreign substance and selectively react to it.
• Mediate by lymphocytes
• 3 types of lymphocytes
1) B Lym
Develop into plasma cells, secrete antibodies
2) T lym
Attack and destroy virus infected cells, regulate other immune cells
3) NK Cells
Destroy virus infected cells and tumor cells
ALL LYM secrete cytokines that act on immune, non immune cells and pathogen
Acquired Immunity 2 Types
1) Passive immunity
Acquire antibodies made by another animal
2) Active immunity
Occur when body expose to pathogen and produce own antibody. Either naturally or artificially
Lymphocytes Mediate the Acquired Immune Response
• Lymphocytes diff by membrane receptors.
• All lym that are specific for a given ligand form a group known as a clone
• At once birth, each clone of lymphocytes is represented by only a few cells, called naïve
• The first exposure to an antigen activates the right clone and stimulates it to divide. clonal
• The newly formed lymphocytes in a clone differentiate into effector cells and memory cells
• Effector cells carry out immediate response, die away in few days.
• Memory cells are long lived, continue reproducing themselves. Subsequent exposure to antigen
activate memory cells and cause rapid clonal expansions
B Lymphocytes Become Plasma Cells and Memory Cells
• Mature B lym insert antibody into cell membranes so they become surface receptors marking the
members of each clone.
• Clone of B cells activate by antigen ->some cells differentiate to plasma cells -> synthesize and
secret antibody but no antibody on surface -> form humoral immunity
• After each invasion, a few memory cells of the clone remain behind, waiting to respond to the
next exposure to the same antigen.
• The primary immune response: occur after initial exposure, slower and lower in magnitude
• The secondary immune response: occur after subsequent exposure, quicker and larger because
it is enhanced by lymphocytes
Antigen -> Upon first exposure to an antigen, naïve lymphocytes reproduce -> clonal expansion ->
short lived effector cells carry out the immediate response -> Memory cells that are left out and long
lived continue to reproduce -> get into secondary immune response when memory cells are reexposed to the appropriate antigen, the clone expands more rapidly to create additional effector
and memory cells.
• 4 polypeptide c