1. DIAGNOSTIC IMMUNOLOGY
IMMUNITY TO INFECTION

2. Major classes of pathogens

3. Definitions
Two organisms live in close association.
 Mutualism: Both members benefit from the association.
e.g., Protozoa live in the gut of termites.
Communalism: When an organism benefits from the host but the host neither benefits nor is harmed.
e.g. Entomoeba gingivalis in human mouth.
*Parasitism: When an organism actually harms its host or lives at the expense of the host.
e.g., Infections with viruses, bacteria, fungi, protozoa, or helminthes.

4. The course of a typical infection and immune responses can be divided into phases
If no innate immunity

5. The establishment of an infection depends on several factors:
Characteristics of the microorganism
Number of organisms
Mode of transmission (how and where they contact the host)
Stability of the organism (in and outside of the host)

6. TYPES OF DEFENSE SYSTEMS
1- Immediate immune response
Complement
Phagocytosis
Natural Antibodies
2- Early immune response
3- Late immune response

7. The Early IR 4-96 hours past infection
1- Macrophages >>>> Cytokines
Increase vascular permeability
Recruits polymorphs and macrophages
Triggers platelets activation
2- Natural killer cells ( Viral infection)
3- Interferon's

8. The Late IR After about 4 days Degradation and Ag presentation
MHC molecules involvement
Activation of T and B lymphocytes
Cellular and humoral response
Specific antibodies

14. Immunity to Bacterial Infection
The first line of defense is NOT dependent on antigen recognition
Innate immunity
Complement activation
Phagocytosis
NK cells

16. Most bacteria are killed by phagocytosis:
Oxygen independent killing
Cationic proteins killing
Acidic pH and lactoferrin
Complement is an effective mechanism but bacteria may be able to avoid complement mediated damage.

19. The second line of defense is characterized by the secretion of specific antibodies;
Neutralize toxins by preventing its binding to the target
Interfere with motility by binding to flagellae
Secretory IgA stops binding to epithelial cells
Aid in targeting complement

20. Immunity To Fungal Infection
Is a growing problem in immunologically compromised hosts
Seen in HIV infection
Seen in cancer patients undergoing chemotherapy
Patients on immunosuppressive drugs
In patients taking long term corticosteroids

21. Fungi infection in human
Little is known about the precise mechanisms involved
Thought to be similar to those against bacteria
Fungi infection in human
Specific mycoses.
Subcutaneous mycoses.
Respiratory mycoses.

22. Activation of macrophages
Proposed mechanisms
Based on cell immunity:
T Helper cells
Cytokines
Activation of macrophages
Elimination of fungi

23. Immunity to Viruses
Viruses are obligate intracellular microorganisms
They require the host cells to drive protein synthesis and metabolize sugar
Viroids are infectious agents that consist of nucleic acids alone
Prions are infectious proteins associated with degenerative neurological diseases of human

26. Innate IR to viral infection
The early stage of the infection is a race between the virus and the host IS
The initial defense is the integrity of the body surfaces
Innate defense system involves;
Interferon
Nk cells
Macrophages

28. Mechanisms involving T cells
CD8+ cells ; These are MHC class 1 restricted cells that focus on the site of virus replication and destroy virus infected cells
CD4+ cells ;
Key factor in defense against viral infection
INF gamma is important for the activation of TNF alpha which induce apoptosis

29. Evading IR by Viruses Mutation
Producing of short stretches of RNA that work against interferon
Production of proteins that inhibit transporting to cell surface such as in infection with CMV

30. Immunopathology of Viral Infection
1- Response to viral infection may cause tissue damage
Ag-Ab complex deposition in kidney and blood >>> inflammatory response >>> T cell mediated damage >> killing of host cells
2- Virus may infect immune cells
3- Viral infection may induce autoimmunity due to antigenic mimicry

31. Immunity to Parasites
Stimulate a number of immunological defense mechanisms
Both humoral and cellular responses
Immune response depends on the stage and the type of infection
Most parasites pass through a complicated life cycle

33. Features of Parasitic infection: 1- Infect large number of people
2- Parasitic infection have common features
Varity and large quantity of Ag
Ability to change their surface Ag
Complicate life cycle
Different mode of entry
3- Most parasites are host specific
4- Host resistance to parasite may be genetic
5- Many parasitic infections are chronic

34. Effector mechanisms by Immune cells
MACROPHAGES
Provide strong defense against small parasites
Secrete factors that kill parasites without ingestion
Secrete cytokines that activate other immune cells
Synthesize nitric oxide that act as parasite toxin
Activation of macrophages is a general feature of early stage of infection

35. NEUTROPHILS
Can kill large and small parasites
Phagocytic activation
Have granules that contain cytotoxic proteins
Have Fc and complement receptors >> ADCC
PLATELETS
Cytotoxic activities against larval stages
Activation are enhanced by cytokines

36. EOSINOPHILS
Characterize parasitic infection
Thought to be specific against tissue parasites
Limit migration of parasites through the host
Less phagocytic than neutrophils
Act in accordance with mast cells

37. Role of T cells
The type of T cells involved is determined by the type and the stage of the infection
Cytokines enhance protective immunity against intracellular parasites
T helper 2 cells are essential for the elimination of intestinal worms

38. Role of Antibodies
Parasites induce production of specific and non specific Abs
Antibodies have several functions on parasites
-Act directly on protozoa
-Block attachment to host cells
-Important for Phagocytosis