Session 1 - Lecture 1 - Type II, III, IV Hypersensitivity Flashcards
1 - Hypersensitivity reactions
Hypersensitivity reactions
“Follow up with what you’ve seen last year by bringing it to the more clinical side of immunology – today we’re talking about hypersensitivity reactions – drive disease, challenge it for the pt, try to manage – double challenges, v important for you to try and understand this concept of hypersensitivity reaction.”
2 - Immune system
Immune system
- Non-self
- Infection
- Altered self
Success Vaccination ADAPTIVE INNATE Protection Prevention
Failure Disease Immunodeficiency (Primary and secondary disorders) Immunological Mechanisms? Autoimmune disease Allergies
“Immune system v efficient w/ dealing with a variety of different insults e.g. non-self, infectious or altered self such as cancerous - It does this to prevent from infection and for memory so subsequent immune reaction is longer and stronger in magnitude. Problem we will talk about today is when the immune system fails – we’ve seen last year examples cases where immune system was failing in case of immunodeficiency (primary and secondary) – major cause of 2nd immunodeficiency in the world, and England – not HIV, but malnutrition – big problem for you guys as well bc in elderly pts >65 y/o, they will be in some way immunodeficient bc of malnutrition. Talk about immune system involved in disease, but today we are seeing it actually driving the disease – e.g. autoimmune disease and allergies – and we will talk about the immunological mechanism – defined as hypersensitivity reactions. So whole of these 2 lectures today will lead to talk about the impact of these abnormal immune responses we call hypersensitivity reaction.”
3 - Harmful effect of the immune system
Harmful effect of the immune system
- Goodpasture’s syndrome
- Haemolytic anaemia
- Systemic lupus erythematosus
- Myasthenia gravis
- Rheumatoid arthritis
- Graves’ disease
“Diseases caused by hypersensitivity reaction – these diseases as you see, some are organ-specific: attack one specific organ, best example is GS – hypersensitivity reaction here is tissue damage leading to glomerulonephritis – other organ specific is HA - agent RBC. Organ specific but change in function such as MG – impaired NMJ associated with weakness and paralysis, or Grave’s disease – hyperreactivity on the thyroid gland. Ans dinally you have a More systemic disease which is clinically very challenging due to the multisystem organ or role being involve – such as SLE - Key feature of SLE is the malor rash shown on face. Hypersensitivity reaction drive difdf type of disease, organ specific – change in function, multi-system organ v important and hard. So 3 qs we want to ask is – type of trigger – whati s actually causing it? What is the immune mechanism? And what is the target (organ or non-organ specific)? Answering these will determine treatment of pts.”
4 - Learning objectives
Learning objectives
• Describe the different types of hypersensitivity reactions
• Understand the different mechanisms of immunological associated with the hypersensitivity reactions
• Appreciate the variety of clinical manifestations driven by the hypersensitivity reactions
• Understand the challenge of treating immunological disorders
“2. understand different mechanisms – very important. 3. Variety of clin manifestations – depend on type of trigger and immune reaction that organ affected.
4. And we will also Understand why really challenging to treat or control/manage pts with disease driven by hypersensitivity reactions.”
5 - Definition
Definition
The term hypersensitivity describes “the antigen-specific immune responses that are either inappropriate or excessive and result in harm to host”
The mechanisms underlying these aberrant immune responses are /those employed by the host to fight
infections/ (!)
“Antigen specific or antigen driven – a trigger against the host to trigger an inappropriate or excessive immune response that will lead to harm to host – harm = change in function or tissue damage. The mechanism that actually drives this aberrant hypersensitivity reaction is the same used against infection against infectious microbes i.e. innate effector component and adaptive effector component. We will describe all the different compoentns responsible for all the diff hypersensivitiy reaction.”
6 - Types of triggers (antigens)
Types of triggers (antigens) • Hypersensitivity to EXOGENOUS antigens Non infectious substances (innocuous) Infectious microbes Drugs (Penicillin) • Hypersensitivity to INTRINSIC antigens Infectious microbes (mimicry) Self antigens (auto-immunity) (!)
“Types of triggers – antigens that actually initiates it:
1a. non infectious microbes such as allergens these are harmless, substances, eat or drink, cause hypersensitivity reaction type I.
1b. Infectious microbes – overreaction of the immune system against gram -ve bacteria - Sepsis! Exaggerated immune response against gram -ve bacteria.
1c. SOme drugs, e.g. penicillin – (most common one to remember but lots of others) – remember but people can be allergic to almost anything (not only medicine).
- The one that is most difficult to maange is diseases caused by INTRINSIC antigens – present qwithin the host.
2a. One that is triggered by infectious mcrobes (molecular mimicry) – host bein response to microbe, immune system reaction against microbe but has constitutional component that is also present in host, so mounting an immune response against microbe will also directly result in response against host.
2b. However one of the most important ones are self-antigens – this will drive autoimmune diseases – reason behind that is v complex, we don’t know why some people and not others, but this will be the most challenging not justin mngmt but also impact and burden for your pt.”
7 - Types of hypersensitivity reactions
Types of hypersensitivity reactions • Type I or immediate (Allergy) > Environmental non infectious antigens • Type II or antiBody mediated • Type III or immune Complexes mediated • Type IV or cell mediated (Delayed) > Environmental infectious agents and self antigens
“remember these
Type I, II and III are antibody-mediated. Type 4 is cell mediated. Type I only mediated by one antibody isotype which is IgE. Type II and III by different antibody isotype - IgG or IgM but type II is against cell-bound antigen (antigen expressed on tissue/cell - cellular); type III against soluble antigen – so complications can occur. Complication of having immune complexes antigen – antigen body formation soluble – deposit and become in system. Type I mostly triggered by innocuous harmless non-infectious antigens (allergens) abut type II or III IV mostly driven by self antigens .Type IV is cell-medaited. Mechanism of atopy.
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