IB Biology notes on infection and the body's responses.

          2. antigen is recognized by helper T-cells that have a receptor that fits the

              particular antigen and is activated

               a. activated helper T-cell produces interleukin-2

                    i. interleukin-2 causes proliferation of certain cytotoxic T cells and B

                       cells

               

                         a. cytotoxic T-cells bind to and produce chemicals that destroy

                             cells that present the particular antigen

Here is an animation:

               b. activated helper T-cell binds to B cells that recognize the same antigen

                    i. there are many parts of the antigen that can be recognized by a T

                       cell, called epitopes

                    ii. therefore, many different B cells can be activated, each

                        producing different antibodies against the same pathogen

                        a. Therefore, against the same pathogen, a number of different

                            antibodies can be made

                         b. since many different B cells produce plasma cells, each capable

                            of cloning itself, this is a polyclonal response

                    ii. B cells divide into many plasma cells

                         a. plasma cell produces antibody that is specific to the antigen

                         b. the antibodies and most of the B cells are gradually lost from

                             the body when they are no longer required

                         c. A small number of B cells remain in the body but are inactive

                             until the same antigen is detected

                              i. called memory B cells

                              ii. Allow a very rapid response upon infection by the same

                                  antigen known as the secondary immune response

                              iii. The reason for vaccination

III. Active versus Passive Immunity

     A. active immunity: immunity that results from the body producing its own    

         antibodies after exposure to a particular antigen

          1. can be induced by vaccination with a microbe that has been treated so

              that it still has antigen but is not able to cause disease

     B. Passive immunity: immunity that results from antibodies that are not self-

         produced but were administered to the individual

          1. is short-lived protection against disease

          2. newborns often have some level of passive immunity because antibodies

              can cross the placenta from the mother and enter the baby's blood

          3. breast-feeding prolongs passive immunity in the baby because some

              antibodies from the mother can be found in her breast milk

          4. can be induced by giving vaccine with antibodies

IV. Vaccination

Here is an animation about constructing vaccines:

     A. goal of vaccination is to produce an immune response without disease

          1. vaccine may contain pathogen that has been treated so that it is less

              virulent,  i.e. Less able to cause disease

               a. often referred to as the attenuated pathogen

          2. vaccine can also contain inactivated toxins

          3. goal is to initiate “challenge and response”

               a. the immune system is challenged by a pathogen and responds by

                   producing antibodies

                    i. since there are many B cells involved in producing the antibodies,

                       this is a polyclonal response

     B. vaccine introduced into the body most commonly by injection (the dreaded

          “shot”)

     C. Vaccination stimulates the primary immune response, hopefully leading to the

         development of the appropriate memory B cells

     D. exposure to the pathogen should stimulate the secondary immune response

         which is faster, stronger and more specific than the primary response

          1. the pathogen should be inactivated or destroyed before the onset of

              disease

Figure 1: Speed of primary versus secondary response.

     E. Benefits of vaccination

          1. total elimination of certain diseases

          2. preventing epidemics/pandemics

          3. decreased health care costs

          4. preventing harmful side effects of disease

     F. Possible dangers of vaccination

          1. Side effects such as soreness near the injection site, low-grade fever

          2. allergic reactions to some of the vaccine's ingredients

               a. e.g. Some vaccines contain egg proteins, yeast proteins,  antibiotics,          

                   (leftover from the production process), human serum albumin (help

                   stabilize live virus), formaldehyde (eliminates the effects of bacterial

                   toxins and makes viruses unable to replicate), aluminum salts (help

                   the vaccine work better), or gelatin that may cause an allergic

                   reaction

          3. a preservative called thimerosol contains mercury and there have been

              concerns about its safety (in the US it “has been removed from or reduced

              to  trace amounts in vaccines for children 6 years of age and younger with

              the exception of the inactivated influenza vaccine” (Iannelli, 2008))

          4. possible overload of the immune system

          5. IB lists possible links to autism but...

For a comprehensive list of side effects for many vaccines, try this website:

     G. So...should you use vaccines?

          1. Personal choice of informed individuals is the key

V. Antibiotics

     A. antibiotic: a chemical that inhibits the growth of microorganisms, particularly

         bacteria

          1. typically work by inhibiting some aspect of bacterial metabolism

               a. inhibition of cell wall synthesis

                    i. most common method

                    ii. e.g. Penicillin, vancomycin,  Bacitracin

               b. inhibition of protein synthesis

                    i. second most common method

                    ii. e.g. Tetracyclines, streptomycin, erythromycin, chloramphenicol

               c. Alteration of cell membranes

                    i. e.g. Bacitracin (topical)

               d. inhibition of nucleic acid synthesis

                    i. e.g. Rifampin, bacitracin

               e. Antimetabolite activity

                    i. e.g. Sulfonamides

*Note that the names of antibiotics is not required for IB but included for interest; I tried to find relatively common antibiotics

V. Monoclonal Antibody Production

Here is a video about monoclonal antibody production:

Here is another address for the same animation of monoclonal antibody production:

     A. monoclonal antibodies: antibodies made by clones of the same B cell

          1. since each B cell makes only a specific antibody, ensures that all the

              antibodies are the same

          2. allows scientist to “harvest” a substantial amount of a single antibody

          3. antibodies obtained from the blood are called polyclonal antibodies

     B. Production of monoclonal antibodies

*Köhler and Milstein devised this technique for mice in 1975 and won a Nobel Prize

Here is an animation of monoclonal antibody production:

          1. B lymphocytes, usually from mice are exposed to a particular antigen

          2. activated B lymphocytes are fused with myeloma cells/bone tumour

              cells/cancerous B cells that divide indefinitely

          3. fused cells are called hybridomas because they are hybrids, one of the

              cells used was cancerous, thus the “-oma” part of the name

     C. Uses of monoclonal antibodies

          1. since they are highly specific, monoclonal antibodies can be used to select

              out/find a specific molecule among many others

               a. diagnose illnesses such as AIDS

               b. identification of blood types and tissue typing for transplant  

                   compatibility

               c. detect substances in the blood such as HCG (human chorionic

                   gonadotrophin) , the hormone that women produce when pregnant

Here is an animation of the home test for pregnancy: __

               d. identify infections

               e. Sort out different T cells

               f. Distinguish between cancerous and normal cells

                    i. thus can be used to carry radioactive isotopes or toxic drugs to kill

                       tumours

               g. Treatments for various illnesses

                    i. emergency treatment of rabies

               h. purification of industrially produced interferon

               i. Detection of certain markers (cardiac isozyme) the are indicative of

                  heart attack

VII. HIV and AIDS

Here is an animation about HIV replication:

Here is an animation about how the HIV infection cycle works:

Here is an animation of treatment of HIV:

Figure 2: How HIV infects a cell.

     A. What is HIV? What is AIDS?    

          1. AIDS: acquired immune deficiency syndrome

          2. HIV: human immunodeficiency virus

               a. causes AIDS

               b. a retrovirus

                    i. genetic material is RNA rather than DNA

               c. Transmitted from human to human via blood semen, vaginal secretions

                   and breast milk

                    i. must “come in contact with a mucous membrane or damaged tissue

                       or be injected directly into the blood-stream (from a needle or

                       syringe) for transmission to possibly occur”

                       ()

                    ii. HIV can also be transmitted via infected blood, infected blood

                        products, organs from HIV infected individuals

          3. Infection by HIV

               a. HIV infects host cell which is the helper T cell

                    i. recall: helper T cells activate B cells to become plasma cells and

                       also stimulate cytotoxic T cells to destroy infected cells and foreign

                       antigen carriers

     

               b. HIV attaches to the helper T cell and injects its RNA and an enzyme

                   called reverse transcriptase into the cell

               c. Reverse transcriptase uses viral RNA as a template to make DNA

               d. viral DNA enters the host nucleus and attaches to the host DNA

                    i. host treats the viral DNA as its own and will transcribe and

                       translate the viral genetic material

               e. Host cell will fill with viral parts which will assemble into viral particles

               f. The infected cell will burst and die, releasing viral particles into the

                   bloodstream to infect other helper T cells

               g. This is essentially the same mechanism as other viruses use however,

                   the important point is that the cells that are infected by this virus are

                   cells that would normally aid in fighting an infection

          4. Consequences of HIV infection

               a. eventually number of helper T cells declines    

               b. infected person is less able to produce antibodies

               c. Immune system functioning is suppressed and opportunistic infections

                   such as pneumonia and Kaposi's sarcoma (a form of skin cancer) may

                   set in

                    i. individuals with normal immune systems can usually fight off these

                       infections

               d. HIV positive: have antibodies against HIV in your blood which indicates

                   that the virus is in your body

               e. AIDS patients are HIV positive and have a T cell count below 200 or

                   are HIV positive and have an opportunistic infection

               f. many AIDS patients die within 2 years of the onset of symptoms but

                  many individuals live for years with no apparent immune complications

     

VIII. BLOOD CLOTTING (same as from Circulatory System package)

     A. Clotting: formation of a solid mass of platelets, red blood cells and fibrin (a protein)

          1. also called coagulation

          2. Fibrinogen: a protein found in blood that is the precursor of fibrin

          3. Prothrombin: inactive form of thrombin found in blood

               a. Vitamin K is necessary for production of prothrombin

          4. Serum: blood plasma without fibrinogen

     B. STEPS IN BLOOD CLOTTING

        

          1. Blood vessel is damaged

          2. platelets clump at the site and partially seal the leak

          3. platelets and damaged tissue release prothrombin activating factor

          4. prothrombin activating factor converts prothrombin to thrombin

               a. requires calcium ions (Ca2+)

          5. thrombin acts as an enzyme that removes 2 short amino acid chains from each end

              of a fibrinogen molecule, making them “sticky”

          6. shortened fibrinogen molecules join end to end forming long threads of fibrin

          7. fibrin threads tangle themselves around the platelets that are plugging the leak

          8. red blood cells are trapped in the network of fibrin and give colour to the clot

                

          9. when repair of blood vessel initiated, the enzyme plasmin destroys fibrin network

A cute video, some details are slightly different from the notes though:

     C. Rewind: Thrombosis

          1. thrombosis: formation of a clot in a blood vessel

               a. often the result of damage to the wall of a blood vessel as in

                   atherosclerosis

               b. other causes are outlined below:

 

References:

Allott and Mindorff. IB Diploma Program Biology Course Companion

Iannelli, 2008.

Mader, Sylvia. Inquiry into Life Seventh edition and Tenth edition.

This article gives detailed information on antibody structure and function including applications of monoclonal and polyclonal antibodies:

This is an interesting site as it is written for the computer sciences and outlines how the study of the immune system is relevant to computer sciences in the introduction.

Review and Practice:

1.  IB Diploma Program Biology Course Companion by Allott and Mindorff:  page 238 #1-7

2. A case study: Clinical Application from

Answer the six questions for homework.