Lecture 12: Adaptive immunity - Clonal Selection of Lymphcytes Flashcards
What are the two branches of the immune response?
Humoral Branch and Cell-Mediated Branch
Humoral Branch involves B cells and antibodies; Cell-Mediated Branch involves T cells.
What does humoral immunity primarily involve?
B cells and antibodies
It is a part of acquired immunity.
What is innate immunity?
Nonspecific immunity
Nonspecific immunity ## Footnote It includes physical barriers, chemical barriers, molecular defenses, cellular defenses, inflammation, and fever.
What are lymphocytes?
T and B cells
hey are antigen-specific and randomly generated.
How many different B and T cells can exist in the human body?
10^12 to 10^16 different B and T cells
What do T cells have that B cells do not?
T cell receptors (TCR)
cells have B cell receptors (BCR).
Define antigen.
A substance that the body sees as foreign or non-self, and to which it mounts an immune response.
What are the most common types of antigens?
Proteins
Some antigens can also be polysaccharides, glycoproteins, or nucleoproteins.
What are epitopes?
Short amino acid sequences recognized by antibodies and T cells (8-20 amino acids).
What is the primary immune response?
The response to the first exposure to an antigen, taking 7-10 days to detect antibodies.
What is the secondary immune response?
The response to a second exposure to the same antigen, occurring within hours to days.
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What are CD4 T cells also known as?
T-helper cells
How do naïve CD4 T cells become T-helper cells?
They recognize their epitope and receive a cytokine signal.
What do T-helper cells do?
Secrete cytokines that direct other immune cells.
What is the role of professional antigen presenting cells (APCs)?
Express class II MHC and present epitopes to naïve CD4 T cells.
What happens to most effector T-helper cells after infection is cleared?
They die, but some become memory T cells.
How do CD8 T cells become cytotoxic T lymphocytes (CTL)?
They must see their specific epitope presented on Class I MHC and receive a cytokine signal.
What do CTL cells do?
Release cytotoxins onto infected target cells.
What is the role of naïve B cells in humoral immunity?
They recognize and bind to epitopes on antigens using the BCR.
What happens to B cells during the primary immune response?
They switch from making IgM to a different isotype as needed.
What is the memory response in B cells?
A faster response (2-3 days) due to memory B cells not needing T cell help.
True or False: Memory T cells need as many signals from professional APCs as naïve T cells to get activated.
False
Which virus causes non-specific overproliferation of B & T cells?
Epstein Barr virus (mononucleosis).
Which enzyme cleaves IgA, and which bacterium produces it?
IgA protease, produced by Streptococcus pyogenes (strep throat).
What do Protein A and Protein G do in bacterial evasion?
Bacteria produce Protein A or Protein G, which flips IgA or IgG around, preventing antibody function (no neutralization, opsonization, or complement fixation).
Which viruses are known to hide antigens?
HSV and measles.
Name a virus, a bacterium, and a protozoan that change their antigens.
Virus: Influenza. Bacterium: Gonococci. Protozoan: Trypanosomes (sleeping sickness).
Which pathogens can reproduce in white blood cells (WBC)?
M. tuberculosis, HIV, and many others.
How does HIV affect CD4 T cells?
HIV kills CD4 T cells, leading to no T helper cells.
What is the result of no activation of B cells due to HIV?
No antibody production, no neutralization of toxins, viruses, or other microbes, decreased opsonization (still have complement), and no complement fixation.
What happens due to no activation of cytotoxic T lymphocytes (CTL) because of HIV?
No killing of infected cells, and no killing of tumor cells.
What are the overall consequences of microbial evasion of adaptive immunity, particularly in the case of HIV?
Opportunistic infections and increased risk of cancer.
