Microbiology 204: Cellular and Molecular Immunology

Microbiology 204: Cellular and Molecular Immunology

Class meets MWF 1:00-2:30PM (*exceptions: no class Fri Oct 10; Wed Nov 26 will be

moved to 11/25 or 11/24)

Lectures are open to auditors

“Flipped sessions” are open to auditors

Discussions are restricted to those enrolled in class (or by permission)

Problem sets and review sessions every other week by our TA: Dan Holohan (Dan.Holohan@ucsf.edu)

Microbiology 204: Cellular and Molecular Immunology

Course web site:http://immunology.ucsf.edu/Micro204schedule

Recommended textbook : Janeway’s Immunobiology;OR Abbas and Lichtman Cellular and Molecular Immunology; OR DeFranco, Robertson, and Locksley Immunity

Grades: 2/3 take-home final and 1/3 participation in discussions

My office hours: Mondays 3-4PM HSE1001E or by arrangement (anthony.defranco@ucsf.edu)

What does the immune system do?

• It protects us from infections with: – 208 viruses– 538 bacteria– 317 fungi– 287 worms– 57 parasitic protozoa (CDC numbers)

• It promotes normal functioning of the body (tissue cleanup, wound repair)

• It removes abnormal cells including malignant ones• But the immune system can also cause disease when it

is not doing the right thing (allergies, autoimmunity, transplant rejection, etc.)

The players• Sentinel cells in tissues

– Dendritic cells, macrophages, mast cells• Circulating phagocytes and granulocytes

– Neutrophils, monocytes, eosinophils, basophils• Lymphocytes: cells which can recognize particular

pathogens (but also can cause allergies and autoimmune diseases)– B lymphocytes: antibodies– T lymphocytes: cell-mediated immunity– (also innate lymphoid cells, NK cells, etc.)

• Tissue cells (epithelial cells, endothelial cells, etc.)

Immune sentinel cells in the tissues: dendritic cells

Langerhans cells (epidermal dendritic cells) in the skinWJ Mullholland et al. J. Invest. Dermatol. 126: 1541, 2006.

Green= dendritic cellsBlue= nuclei of all cells

TNF

or dendritic cell

Inflammatory mediators:-Lipids (prostaglandins, etc.)-Proteins (cytokines/chemokines)

Others

Inflammatory mediators are made in response to detection of infection or injury

Cytokines and Inflammation

• Pro-inflammatory cytokines are many, but especially important: TNF, IL-1, and IL-6

• TNF and IL-1 signal to endothelial cells to make them:– Leaky to fluid (influx of plasma; containing antibodies,

complement components, etc.)– Sticky for leukocytes, leading to influx of leukocytes

• IL-6 promotes adaptive immune responses; systemic effects

Leukocyte recruitment to sites of inflammation

or DC

The neutrophil is the immune system’s first responder

• Neutrophils are typically the first white blood cells to come into a site of acute inflammation

(PLAY MOVIE HERE): Lammermann et al. Nature 498: 371-5, 2013.

Phagocytosis and Killing of Microbes

Abbas et al. Fig. 2-17

Innate Immunity vs. Adaptive immunity

• Innate immunity utilizes evolved recognition mechanisms and is surprisingly effective, but changes little based on life experience

• In innate immunity, limited numbers of distinct receptors; recognize highly conserved features of classes of microbes.

• Adaptive immunity learns from previous experience and hence can protect better upon a second infection by the same agent.

• Adaptive immunity has a very large number of distinct “antigen receptors” of T and B lymphocytes; generated by DNA rearrangements in each developing lymphocyte; clonal selection of lymphocytes that recognize an infecting agent

Many different antibodies are created by combinations of gene segments

Adaptive Immunity: Antibodies I

• A molecule that induces the production of an antibody is called an “antigen”

• A few B cells that recognize the infectious agent become activated, each multiply to form a “clone”.

• These progeny then become antibody-secreting factories.

Generation of lymphocytes of many specificities

Clonal deletion to remove self-reactive lymphocytes

Clonal selection to expand pathogen-reactive lymphocytes during an immune response

The Clonal Selection Hypothesis

Antibody responses proceed in two phases

Goodnow et al, Nature Immunol. 2010

Adaptive Immunity: Antibodies II

• Rapid production of lower affinity antibody made by short-lived plasma cells

• Slower “germinal center response” selection for higher affinity gives rise to long-lived plasma cells

• Rational design of the “conjugate vaccines” (starting in the 1990s)

Antibodies bind antigens

Two protein components: heavy chain and light chain; can come in 5 varieties of heavy chains:IgM, IgG, IgA, IgE, IgD

Antibodies can be directly protective or can promote immune protective mechanisms via other cells or

molecules

neutralization activation of complement

Adaptive Immunity: Antibodies III

• “Active immunity” (infection, vaccination)

• “Passive immunity”: maternal transfer of IgG across placenta; injection of antibodies to protect against infections, toxins; IVIG for immunodeficiency

• “Monoclonal antibodies” for passive immunity, therapy, diagnosis. All identical more standardized therapeutic or diagnostic.

• To work well as therapy, need to make as human as possible; many new MAb therapeutics in the last 10 years. Most are to treat cancers or to suppress immune responses

Monoclonal antibodies used in medicine

Standardized, unlimited reagents for diagnosis or therapy

Some representative examples. This list is rapidly expanding in recent years

CD Nomenclature

• Structurally defined leukocyte surface molecule that is expressed on cells of a particular lineage (“differentiation”) and recognized by a group (“cluster”) of monoclonal antibodies is called a member of a cluster of differentiation (CD)

• CD molecules (CD antigens, CD markers) are:• Identified by numbers• Used to classify leukocytes into functionally

distinct subpopulations, e.g. helper T cells are CD4+CD8-, CTLs are CD8+CD4-

• Often involved in leukocyte functions• Antibodies against various CD molecules are used to:• Identify and isolate leukocyte subpopulations• Study functions of leukocytes• Eliminate particular cell populations

The TCR of CD4+ and CD8+ T cells recognizes MHC-bound peptide + portions of the MHC.

Other T cells ( gd T cells, NKT cells) recognize non-peptide antigens; these are small cell populations whose function is unclear.

Recognition of antigen by the TCR

Peptides are bound to MHC molecules and presented to T cells

MHC=major histocompatability complex. HLA=human leukocyte antigen

Killer T cells and Helper T cells

killing

cytokines

helper

Microbe evadesKilling

Adaptive Immunity: Anatomy of the response

• Naïve T cells and B cells recirculate between lymph nodes, spleen, and the blood.

• Antigen is taken to the lymph node either by the flow of lymph or is carried by a maturing dendritic cells that migrate along the lymphatics.

• The dendritic cell presents antigen to naïve T cells in the lymph node.

Role of costimulation in T cell activation

Immune responses are tailored to the type of infection

• Defense against extracellular microbes: IgM, IgG and Th17• Defense against microbes that survive and replicate inside

phagocytes (macrophages and monocytes): “type 1 immunity” (Th1)

• Defense against viruses:– early defense: innate mechanisms that restrict virus replication

(interferon, etc.)– Adaptive immune defense: antibodies which block virus

infection of cells (“neutralizing antibodies”) plus cytotoxic T cells

• Defense against worms and biting insects: “type 2 immunity” (IgE, Th2), Manifestations include: sneezing, coughing, itching, diarrhea, tears, etc. (allergies and asthma mostly involve this type of immune response)

Innate Lymphoid Cells: Parallels to T cell subsets

Spits and DiSanto, Nature Immunology 12: 21-27, 2011

IL-5

Immune system and chronic inflammation

• Sterile inflammation (tissue injury but no infectious agent present): innate recognition of tissue damage

• Chronic inflammation: if antigen persists, antigen-reactive T cells can drive continued inflammation, which can cause tissue damage (autoimmune diseases and inflammatory diseases)

• Likely important role of inflammation in pathogenesis of chronic diseases: atherosclerosis, type 2 diabetes, probably Alzheimer’s disease, cancer (can be positive or negative)

Anti-CTLA-4 antibody is approved for tumor immunotherapy (enhancing immune responses against tumors) Even more impressive results with anti-PD-1 in cancer patients; combination trials recently reported

Therapeutics based on the B7:CD28/CTLA-4 family 2. Removing the brakes on the immune response

Blocking the PD-1/PDL-1 pathway to enhance tumor immunity