PROF STEIN LECTURE 9-IMMUNE SYSTEM

WHAT ARE THE KEY PLAYERS INSITE THE BODY FOR INNATE IMMUNITY?

LEUKOCYTES

WHAT IS INNATE IMMUNITY (7 POINTS)?

• FIRST-BARRIERS TO INVASION

• SECOND-RECOGNITION OF NON-SELF PROTEINS (ANTIGENS) FROM VIRUS, BACTERIA, FUNGUS, PROTISTS AND RESPOND

• LEUKOCYTES (WHITE BLOOD CELLS)

• GENERIC RESPONSE-BROAD RECOGNITION OF ANTIGENS BY TOLL-LIKE RECEPTORS (TLRs; AT LEAST 10), A SUBSET OF PATTERN RECOGNITION RECEPTORS, ON LEUKOCYTES

• ANTIGEN BINDS TO TLR AND ACTIVATES INTRACELLULAR TRANSCRIPTION FACTORS

• FAST…”READY TO GO” AT TISSUE/BLOOD LEVEL BUT CAN BE DANGEROUS-TISSUE DAMAGE/SEPSIS

• VERY IMPORTANT ROLE IN ACTIVATING ADAPTIVE IMMUNE RESPONSE

INFLAMMATORY RESPONSE: WHAT IS A MACROPHAGE?

• BIG EATER-ALONG WITH OTHER CELLS SECRETE CYTOKINES THAT CAUSE SWELLING AND FEVER, STIMULATE LEUKOCYTE MITOSIS (ELEVATE WHITE BLOOD CELL COUNT); INCREASE FIRING IN NEURONS CARRYING PAIN SIGNALS

• MORE FORM FROM WHITE BLOOD CELLS (THROUGH MITOSIS WHERE THEY DIVIDE)

INFLAMMATORY RESPONSE: WHAT IS CYTOKINE STORM?

• OVERLY AGGRESSIVE IMMUNE RESPONSE CAN BE LIFE THREATENING, PLAMA LEAVES BLOOD AND ENTERS EXTRACELLULAR SPACE, BLOOD PRESSURE DROPS, INCREASED FLUID CAUSES SWELLING, DIFFUSION BARRIER AND TISSUE DAMAGE

INFLAMMATORY RESPONSE: WHAT ARE MAST CELLS?

• SECRETE HISTAMINE (DILATE BLOOD VESSELS)

INFLAMMATORY RESPONSE: WHAT ARE NEUTROPHILS?

• FOLLOW CHEMOKINE TRAIL FROM BLOOD TO TISSUE; REMOVE PATHOGEN

WHAT IS THE CYTOKINE STORM AS IT RELATES TO CV AND RESPIRATORY SYSTEMS?

• PLASMA LEAKING OUT OF BLOOD VESSELS DECREASES BLOOD VOLUME

• LESS BLOOD VOLUME MEANS LESS STROKE VOLUME ON EVERY BEAT

• LESS STROKE VOLUME ON EVERY BEAT MEANS LESS CARDIAC OUTPUT

CYTOKINE STORM AS IT RELATES TO CV AND RESPIRATORY SYSTEMS: WHAT HAPPENS TO BLOOD PRESSURE?

• IT DECREASES

CYTOKINE STORM AS IT RELATES TO CV AND RESPIRATORY SYSTEMS: WHAT WOULD THE COMPENSATIONS IN THE CV SYSTEM BE?

• MORE SYMPATHETIC ACTIVITY

• INCREASED HEART RATE

IF EXCESS FLUID VOLUME IN LUNGS INCREASES DISTANCE BETWEEN AIR IN ALVEOLI AND HEMOGLOBIN IN RED BLOOD CELL; WHAT HAPPENS TO BLOOD PO2?

• IT WOULD DECREASE MEANING THE OXYGEN LEVEL IN THE BLOOD WILL DROP, AS INCREASED DISTANCE HINDERS THE EFFICIENT DIFFUSION OF OXYGEN FROM THE ALVEOLI TO THE BLOODSTREAM

• CAUSE CO2 IS 2X MORE SOLUBLE

WHAT IS INFLAMMATIONS’ 4 MAIN TERMS?

• CALOR, DOLAR, RUBOR, TUMOR

• HEAT, PAIN, REDNESS, SWELLING

WHAT IS INFLAMMATION (3 POINTS)?

• SEEN ON SURFACE OF SKIN

• CAN ALSO BE PRESENT THROUGHOUT BODY AND CONTRIBUTE TO A HOST OF DISEASES AND DISORDERS (SARS, ARTHRITIS, ASTHMA, CROHN’S DISEASE, CARDIOVASCULAR DAMAGE, ALZHEIMER’S)

• IN LUNG TISSUE, SWELLING LIMITS DIFFUSION BY INCREASING DISTANCE BETWEEN AIR AND BLOOD AND DAMAGES TISSUE REDUCING SURFACE AREA

WHAT ARE THE KEY PLAYERS OF ADAPTIVE IMMUNITY?

• LYMPHOCYTES

WHAT IS ADAPTIVE IMMUNITY?

• THERE ARE 2×10^12 LYMPHOCYTES IN THE HUMAN BODY WHICH IS ABOUT THE SAME MASS AT THE LIVER

• B CELLS MATURE IN BONE MARROW AND T CELLS MATURE IN THYMUS GLAND AND MIGRATE TO SPLEEN AND LYMPHATIC SYSTEM

WHAT ARE THE TWO TYPES OF RECEPTORS THAT RECOGNIZE ANTIGENS?

1) IMMUNOGLOBULINS, WHICH ARE ANTIBODIES+B-CELL RECEPTORS

2) T-CELL RECEPTORS

WHAT ARE ANTIBODIES?

• FLOAT FREE IN THE BLOOD OR THEY ARE BOUND TO B-CELL MEMBRANES WHERE THEY ARE CALLED B-CELL RECEPTORS. COLLECTIVELY THESE ARE REFERRED TO AS IMMUNOGLOBULINS.

WHAT ARE T-CELL RECEPTORS?

• SIMILAR IN STRUCTURE TO “ARMS” OF ANTIBODIES AND BCRS

WHAT DO YOU HAVE IN YOUR BODY RIGHT NOW THAT CAN BIND TO ALL ANTIGENS THAT EXIST IN THE WORLD?

• B-CELL RECEPTORS (BCRS)

• T-CELL RECEPTORS (TCRS)

WHAT IS AN EPITOPE?

• THE SPECIFIC REGION OF THE ANTIGEN PROTEIN THAT IS RECOGNIZED AND BOUND

HOW DID YOU GET THIS DIVERSE GROUP OF PROTEINS?

DNA RECOMBINATION=DIVERSITY

• DNA RECOMBINATION IS A COMMON OCCURRENCE (CROSSING OVER, RECOMBINATION FREQUENCIES AND GENE MAPPING)

• DNA RECOMBINATION IN B AND T CELLS LIMITED TO SPECIFIC SECTIONS OF DNA WITHIN SPECIFIC GENES (BCR AND TCR GENES) THAT CODE FOR VARIABLE REGIONS OF THE RECEPTOR

  • V (VARIABLE), J (JOINING) AND D (DIVERSITY) SEGMENTS UNDERGO DNA RECOMBINATION

  • ALMOST LIMITLESS NUMBER OF COMBINATIONS CODE FOR A VARIETY OF PROTEINS THAT BIND ALMOST LIMITLESS NUMBER OF ANTIGENS

WHAT IF THIS RANDOM RECOMBINATION RESULTS IN B AND T CELLS THAT RECOGNIZE ANTIGENS ON YOUR OWN CELLS?

• THESE CELLS ARE SILENCED DURING THIS PROCESS

• SILENCING IS NOT ALWAYS COMPLETE AND AUTOIMMUNE DISEASES MAY ARISE

WHAT IS DNA RECOMBINATION = TO?

RECEPTOR DIVERSITY

• DNA RECOMBINATION IS TARGETED TO B AND T CELL RECEPTOR GENES

• THE SEGMENTS OF DNA WITH THE HIGHEST RATE OF RECOMBINATION ARE THOSE THAT CODE FOR THE VARIABLE REGIONS OF THE RECEPTOR

WHAT HAPPENS AFTER UNIQUE PATTERNS OF RECOMBINATION?

• SUBSEQUENT CELL DIVISIONS PRESERVE THE UNIQUE DNA; BCR AND TCR GENES IN B AND T CELLS. THERE ARE 10^14 DIFFERENT TYPES OF THESE CELLS!

WHAT CELLS HAVE UNIQUE DNA?

• B-CELLS AND T-CELLS

• BCR AND TCR GENES ARE DIFFERENT IN EACH OF THE 2×10^14 DIFFERENT TYPES OF THESE CELLS

OTHER CELLS USE ALTERNATIVE SPLICING OF RNA TO GET DIVERSITY OF PROTEINS. WHY NOT USE THIS SYSTEM FOR BCRS AND TCRS?

• REQUIRES ENZYMES TO DO WORK/MANIPULATE THE mRNA/A LOT MORE RESOURCES

WHAT ARE THE 2 WAYS ALTERNATIVE SPLICING PLAYS A ROLE IN B-CELLS?

1) FULL TRANSCRIPT YIELDS A PROTEIN WITH TRANSMEMBRANE DOMAINS=MEMBRANE-BOUND B-CELL RECEPTOR

2) ALTERNATIVE SPLICING OF TRANSCRIPT YIELDS A PROTEIN THAT LACKS THE TRANSMEMBRANE DOMAINS = FREE FLOATING ANTIBODY

WHAT IS T-CELL ACTIVATION (4 POINTS)

• DENDRITIC CELLS INGEST ANTIGEN FIRST

• ANTIGEN IS DIGESTED INTO PEPTIDE FRAGMENTS

• PEPTIDE FRAGMENTS ARE COMBINED WITH MHC PROTEIN (MAJOR HISTOCOMPATIBILITY PROTEIN)

• MHC-PEPTIDE PRESENTED ON SURFACE OF MEMBRANE FOR T-CELLS

WHAT ARE THE 4 POINTS OF DENDRITIC CELL ACTIVATION: MHC PROTEINS?

• MHC PROTEINS WERE NAMED FOR THEIR ROLE IN TISSUE REJECTION IN TRANSPLANT SURGERIES

• MHC PROTEINS PRESENT PROTEIN FRAGMENTS NATIVE TO THE ORGANISM TO SIGNAL WHICH PROTEINS ARE “SELF” TO ADAPTIVE IMMUNE SYSTEM

• MHC PROTEINS ALSO PRESENT FOREIGN PROTEIN FRAGMENTS TO ACTIVATE ADAPTIVE IMMUNE SYSTEM

WHAT IS T-CELL ACTIVATION (3 POINTS)?

• ONE TYPE OF T-CELL (OUT OF 2×10^12 TYPES) RECOGNIZES MHC-PRESENTED PEPTIDE AND ACTIVATES

• CLONAL EXPANSION OF SPECIFIC T-CELL AND HELPER T-CELLS

• THAT ONE TYPE OF T-CELL, OUT OF 2×10^12 TYPES, UNDERGOES MITOSIS

WHAT IS B-CELL ACTIVATION?

• ONE TYPE OF B-CELL (OUT OF 10^14 TYPES) RECOGNIZES ANTIGEN—>THAT ONE TYPE OF B-CELL OUT OF 2×10^14 TYPES IS ACTIVATED

  1) BINDS ANTIGEN TO ACTIVATE, INTERNALIZES ANTIGEN, COMBINES WITH MHC PEPTIDE AND PRESENTED ON SURFACE OF MEMBRANE (GETS HELPER T-CELLS INVOLVED)

  2) ONCE ACTIVATED, UNDERGOES CLONAL EXPANSION (REPLICATIONS, INC. MITOSIS) COUPLED WITH SOMATIC HYPERMUTATION IN VARIABLE REGION (UP TO ONE MILLION GREATER MUTATION RATE) LEADING TO “AFFINITY MATURATION”, BETTER BINDING TO ANTIGEN

  3) MORE B-CELLS TO FIGHT PATHOGEN; MORE FINELY TUNED ANTIBODIES (BETTER RECOGNITION OF ANTIGENS ON PATHOGENS)

WHAT IS INNATE AND ADAPTIVE IMMUNE SYSTEM FUNCTION OVERLAP (5 POINTS)

• NATURAL KILLER, OR “NK” CELLS ARE PART OF THE INNATE AND ADAPTIVE IMMUNE SYSTEM

THEY…

• FORM IN BONE MARROW AND SPLEEN BUT CIRCULATE AS PART OF THE INNATE IMMUNE SYSTEM LIKE LEUKOCYTES

• THEY CAN IDENTIFY AND KILL CELLS CONTAINING VIRUSES AND FOREIGN CELLS WITHOUT ADAPTIVE IMMUNE SYSTEM ANTIBODIES

• WORK WITH ADAPTIVE IMMUNE SYSTEM

• PLAY A MAJOR ROLE IN REJECTION OF TRANSPLANTED ORGANS

WHAT ARE IMMUNIZATIONS (3 POINTS)

• FIRST EXPOSURE TO PATHOGEN RESULTS IN FULL BLOWN ILLNESS AS IT TAKES TIME TO ACTIVATE ADAPTIVE IMMUNITY BUT A MEMORY OF ANTIGEN IS KEPT TO PREVENT FUTURE INFETION

• DELIERATE INJECTION OF ANTIGENS VIA DEAD, INACTIVATED VIRUSES OR BACTERIA GIVES IMMUNE RESPONSE AND MEMORY WITHOUT ILLNESS

• INDIVIDUAL IMMUNITY (PERSONAL BENEFIT) AND HERD IMMUNITY (BENEFITS SOCIETY… “GET YOUR FLU SHOT TO SAVE YOUR GRANDPA’S LIFE”)

WHAT ARE SOME PROBLEMS FACED WHEN DEVELOPING A VACCINE (4 POINTS)?

• THE NUMBER OF POSSIBLE EPITOPES TO TARGET FOR DEVELOPMENT OF IMMUNIZATIONS IS VAST

• ONLY SOME PROTEINS ARE ESSENTIAL (“SPIKE” PROTEINS IN SARS-COV2 VIRUS THAT ALLOW IT TO ENTER CELLS) AND AN EFFECTIVE VACCINE MUST TARGET THE RIGHT ONES

• IF YOU TARGET ONE EPITOPE ON ONE PROTEIN FOR A VACCINE THE VIRUS CAN “MUTATE ITS WAY AROUND” THAT VACCINE (FLU VACCINES TYPICALLY TARGET 2 EPITOPES SO SINGLE MUTATION WOULD NOT RENDER THE VIRUS “INVISIBLE” TO THE IMMUNE SYSTEM)

• LENGTH OF IMMUNITY VARIES GREATLY

WHAT IS SILICO PREDICTION?

• USE OF COMPUTATION TO SPEED UP VACCINATION RESEARCH

• IDENTIFY AN EPITOPE OR TWO ON AN ESSENTIAL PROTEIN TO TARGET

  • “Fortunately, researchers have developed in silico prediction methods that dramatically
    reduce the burden associated with epitope mapping by decreasing the list of potential
    epitope candidates for experimental testing.”

• FIND AN EPITOPE THAT BINDS TO MHC PROTEINS (THIS IS A BIG PROBLEM)

  • NOT ALL PEPTIDES BIND WELL TO MHC (AKA HUMAN LEUKOCYTE ANTIGENS OR HLAS)

  • MHC, OR HLA, MOLECULES VARY AROUND THE WORLD WITH DIFFERENT EXPRESSION IN DIFFERENT ETHNIC GROUPS, BUT THERE ARE “SUPERTYPES” THAT ARE ARE EXPRESSED IN MOST INDIVIDUALS

  • “Identification of promiscuous peptide-binding to HLA supertypes enables the development of T-
    cell epitope vaccines with high-population coverage using a limited number of peptides.”

• INNATE IMMUNE SYSTEM MUST BE CO-ACTIVATED (SYNTHETIC MOLECULE ADJUVANTS) ALONG WUTH INOCULATION WITH EPITOPE PEPTIDE

  • “it should be borne in mind that epitope peptides exhibit little immunogenicity and need
    to be used in combination with adjuvants, which increase immunogenicity by inducing
    strong innate immune responses that enable adaptive immunity”

WHAT ARE THE MEASLES VIRUS COMEBACKS (4 POINTS)?

• THE US IS CURRENTLY EXPERIENCING A SIGNIFICANT RESURGENCE!

• “DURING 1989 TO 1991, A RESURGENCE OF MEASLES IN THE US RESULTED IN MORE THAN 100 DEATHS AMONG >55,000 CASES REPORTED, REMINDING US RESIDENTS OF THE POTENTIAL SEVERITY OF MEASLES, EVEN IN THE ERA OF MODERN MEDICAL CARE”

• “THE US WITNESSED THE RETURN OF SUBACUTE SCLEROSING PANENCEPHALITIS AMONG US CHILDREN, A RARE, FATAL NEUROLOGIC COMPLICATION OF MEASLES THAT HAD ALL BUT DISAPPEARED AFTER MEASLES VACCINE WAS INTRODUCED IN THE 1960S”

• “AS A RESULT OF HIGH VACCINATION COVERAGE, MEASLES ELIMINATION (THE ABSENCE OF ENDEMIC TRANSMISSION) WAS ACHIEVED IN THE US IN THE LATE 1990S AND LIKELY IN THE REST OF THE AMERICAS SINCE THE EARLY 2000S”

WHAT IS MEASLES HISTORY (LAST SLIDE)?

• MEASLES IS A DEADLY AND DEBILITATING DISEASE

• 27 YEARS AGO IMMUNIZATIONS PREVENTED THIS DISEASE IN THE US, BUT AROYND THE WORLD THE STORY WAS DIFFERENT

• LOOK AT DIAGRAM