Defence against infectious disease (AHL)

12.1     Agents that cause infectious disease

12.1.1     Define pathogen.

12.1.2     State one example of an infectious disease caused by members of each of the following groups: viruses, bacteria, fungi, protozoa, flatworms and roundworms.

12.1.3     List six methods by which disease-causing agents are transmitted and gain entry to the body.

Note that this is simple a list and no descriptions or details of methods are required.

12.1.4     Describe the cause, transmission and social implications of AIDS.

AIDS is selected as one syndromic condition where the immune system fails and opportunistic pathogens cause further harm. An initial study will have been made in SSC 5.3 but here is the opportunity to go into greater depth. There is a direct link here with 12.2.8 as the ELISA test for HIV antibodies in the plasma uses a monoclonal antibody. Furthermore the biology of the HIV retrovirus with its RNA and reverse trancriptase makes an interesting link with 8.3.7.

12.2.1     Describe the process of clotting involving, thrombokinase, prothrombin, Ca²⁺ ions, fibrinogen, platelets and vitamin K.

12.2.1     Describe the process of clotting involving, thrombokinase, prothrombin, Ca²⁺ ions, fibrinogen, platelets and vitamin K.

No further details are required of the clotting factors though there is an obvious link to 10.6.7 with the transfer of the gene factor IX into sheep.

12.2.2     Outline the principle of challenge and response clonal selection and memory cells as the basis of immunity.

That is intended to be a simple introduction to the complex topic of immunity. Here the idea of a polyclonal response can be introduced.

12.2.3     Define active immunity

12.2.4     Define passive immunity

12.2.5     Define natural immunity

12.2.6     Define artificial immunity.

12.2.7     Explain the roles of B-cells, MHC, helper T-cells, cytotoxic T-cells, memory cells and immunoglobulins in the in the antigen/antibody response.

This section is clearly going to take up a high proportion of the suggested 4 hours. Candidates are not expected to know about Class I, II and III MHC proteins, but should be given a simplified account of the role of MHC protein in cell recognition, and antigen presentation. Reference should be made to both the humoral response and the cellular response. Students should also be aware of the five classes of immunoglobulin, IgA, IgD, IgE, IgG and IgM and their respective roles in the immune response.

Activation of B-cells into plasma cells cross-links well with the role of rER in protein synthesis covered in SSC 1.3 and AHL 7.3.

12.2.8     Describe the production of monoclonal antibodies and one use in diagnosis and one use in treatment.

Detection of antibodies to HIV is one example of diagnosis. Others are detection of a specific cardiac isoenzyme in suspected cases of heart attack, or a well known one is detection of HCG in pregnancy test kits. (Cross reference 11.2.2). Examples of the use of monoclonal antibodies for treatment could be: targeting of cancer cells with drugs attached to MCB’s; emergency treatment of rabies or cancer; blood and tissue typing for transplant compatibility; purification of industrially made interferon.

12.2.9     Explain the need for immunisation against the bacterial infections: diphtheria, whooping cough and tetanus, and against the viral infections: measles polio and rubella.

The role of memory cells should be emphasised here. The primary and secondary responses can be clearly illustrated by a graph. Precise details of all types of vaccine-attenuated virus, inactivated toxins, etc., for specific disease is not required.

12.2.10     Outline the process of immunisation.

12.2.11     Discuss the benefits and danger of immunisation against bacterial and viral infection.