The Immune system. Role: protect body against pathogens Pathogens; bacteria, bacterial toxin, viruses, parasites, and fungi. Outline. Anatomy of the Immune system Organization of the body’s defenses Humoral immunity Cell-mediated immunity Immune responses in Health and diseases. Outline.
Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.
- Phagocytes (phagocytosis): neutrophils, eosinophils, monocytes, macrophages, dendritic cells (skin)
- Lymphocytes: Bs and Ts, natural killer cells
- Mast cells
- primary lymphoid tissues (bone marrow and thymus)
- secondary lymphoid tissuesAnatomy
Non-specific defenses: no need to decipher pathogen’s identiy. Always present in the body.
- Physical barriers
- Natural cell killers (NK cells)
- Complement system
Specific defenses:Based onn recognition of the pathogen’s identity
Cell-mediated immunityOrganization of the body’s defenses
Physical barriers identiy. Always present in the body.
- stream of tears or urine
pH (stomach, vagina)
enzymes (stomach, tears)
Complement systemNon-specific defenses
Symptoms of inflammation:
About 30 blood proteins identiy. Always present in the body.
They become activated either by direct contact with a pathogen or by contact with a bound antibody.
In an activated state, they form a complex which opens a hole in a pathogen’s cell membrane bacterial lysis
Complement system also promotes inflammationComplement system
Cytotoxic T cells, lacking markers identiy. Always present in the body.
Able to recognize a wide range of pathogens without prior exposure
When recognition and binding occur, the NK cells destroy the pathogen through cell lysisNatural Killer cells = NK cells
Diversity: Any shape can be recognized by a B or T-lymphocytes and trigger an immune reaction
Memory: once a pathogen has activated the immune system, memory cells remain and will protect against a secondary infection
Self-tolerance: the immune system does not attack itselfSpecific immunity
Macrophages (antigen presenting cell = APC): phagocytize pathogens and present antigens to helper-T lymphocytes
Helper-T lymphocytes: secrete lymphokines and activate B and killer T lymphocytes
B-lymphocytes: multiply and specialize into plasma cells secrete antibodies
Killer-T lymphocytes: kill (through lysis) infected or cancerous cellsSpecific immunity = the players
1- Macrophages phagocytize a pathogen and present an antigen to a matching helper-T cell
2- At the same time, some pathogens contact B-cells matching the pathogen’s antigens
The helper-T cells multiply, secrete lymphokines which stimulate the B-cells to multiply and specialize into plasma cells
The plasma cells secretes antibodiesAntibody-mediated (humoral) immunity = AMI
Figure 23.7 to a matching helper-T cell
Structures formed by 4 proteins to a matching helper-T cell
Two main regions:
the upper region is highly variable and bind to a specific shape (the antigen)
The base region is constant for all antibodies this region, when the antibody is bound to its antigen, activates the complement systemWhat are antibodies?
Once a T, B or killer lymphocytes have made contact with their specific antigen, they are triggered into action but they also divide and form a large amount of identical cells, called a clone.Clonal selection
Since over a millions of different types are needed, how can the DNA in the nucleus code for each of them? There is clearly not enough DNA to accomplish that.
During embryogenesis, several genes coding for the variable portion of the antibody (and each responsible for part of a shape) reshuffle so each combination of genes codes for a specific antibody (and shape). So a stem cell receives the capability to form one single type of antibody.
Once formed, they circulate in the body. If they meet and bind to a shape (formed by a protein) present in the body, they are destroyed or deleted, so that only the stem cells responsible for antibodies aimed at foreign pathogens are left.
A stem cell able to react with our own proteins and not deleted during fetal life might later trigger an autoimmune disease.Clonal deletion
Figure 23.11 (1 of 2)
- Active and natural
- Active and artificial
- Passive and natural
- Passive and artificial
Immediate allergic reaction: due to IgE antibody?
Tissue transplant and tissue rejection: due to cytotoxic T cellsClinical applications
Delayed allergic reaction:
due to cytotoxic T cells