Multi-System Autoimmune Disease Flashcards
What is the sequence of events in autoimmunity?
Initiating event + genetic susceptibility Breakdown of self-tolerance Auto-reactivity Humoral +/- cellular Autoimmune disease
What is involved in the susceptibility for the development of autoimmune disease?
Multifactorial
Involves interaction of internal factors e.g. genes, hormones, immune dysregulation with exogenous factors e.g. infections, drugs, UV radiation
When combined together, the initiating exogenous factors in an inherently susceptible individual leads to a breakdown of damaging immune response and ultimately tissue or organ damage
- genetic/regulatory/hormonal/environmental/other factors
- breakdown of immunological tolerance
- pathological autorecognition
- inflammation and tissue damage, autoimmunity, hypersensitivity
Autoimmune diseases are conventionally organised into what?
Those which are predominantly organ specific i.e. where the aberrant immune response is directed against self-antigens which are localised or confined to particular tissues
Non-organ specific i.e. where the immune response is directed against self-antigens which have a more widespread, ubiquitous distribution
Some diseases in the middle of the spectrum tend to have a mixture of both organ-specific and non-organ specific immunopathology
The connective tissue disorders are all at the non-organ specific pole of the spectrum
What is involved in immune pathology?
Autoimmunity
Hypersensitivity
Immune deficiency
What are the functions of the complement system?
Phagocyte chemotaxis
Opsonisation
Lysis of micro-organisms
Maintaining solubility of immune complexes
The complement system is a component of what immune system?
Innate
What does the complement system comprise?
Collection of serum proteins organised into a classical pathway, an alternate pathway and a terminal pathway
Control of proteins in the serum and body fluids which prevents inappropriate complement activation, or down regulate and turn off complement activation
Series of cell surface control proteins which control and regulate the activity of the complement pathway
What is the classical pathway activated by?
Immune complexes containing IgG and IgM
Antigen bound IgM is particularly effective at classical pathway activation
The alternate pathway cycles constantly at what rate?
Very low rate of physiological activity
What is the alternate pathway up-regulated by?
A number of factors, including exposure to endotoxin-producing micro-organisms
At what point do the classical and alternate pathways converge?
At the point of breakdown of C3 into its breakdown products C3a and C3b
What happens in the terminal pathway?
C5 is broken down into C5a and C5b and the components C6, C7, C8 and C9 sequentially bind to C5b to form a multi-molecular C5b-C6-C7-C8-C9 complex called the membrane attack complex
In what diseases are the opsonisation function and maintenance of immune complex solubility of focal importance?
Connective tissue disease, particularly those where abnormal production, handling and deposition of immune complexes are involved in disease pathogenesis
Employment of complement measurements has three principle areas of importance in connective tissue disease, what are these?
Diagnosis
Monitoring
Detection of hereditary deficiencies
What do complement components roughly reflect?
The amount of immune complexes being generated, the more immune complexes being produced during disease exacerbation the more complement is consumed and the lower the measured levels
What happens to complement as diseases go into remission?
Immune complex production decreases and complement levels rise
Measuring complement levels can therefore be useful in disease diagnosis and in the monitoring of disease activity
In what disease is complement measurement of little practical value?
In diseases such as RA which are caused mainly by cellular mechanisms with only a small pathogenic component of localised immune complex formation
The use of complement tests for consideration and detection of hereditary complement deficiencies is principally a reflection of what?
The important role of classical pathway components (C1, 2 and 4) and their breakdown products in opsonisation and maintaining the solubility of immune complexes, and in preventing their pathological deposition into tissues
What happens when there are genetic deficiencies of one or more classical pathway component?
Immune complexes being produced in the course of a normal reaction to infection/dietary proteins etc. cannot be dealt with by normal pathological mechanisms and so readily deposit out of solution into tissues e.g. kidneys, joints and skin
Damage is therefore not the result of inappropriate and excessive immune complex formation but rather an inability to handle and dispose of even normal levels of immune complex formation
In classical pathway deficiencies, what is a major clue that the mechanistic problem lies within the complement system rather than ANA autoantibody production?
Patients are ANA negative
What are the features of complement deficiency?
Genetic deficiencies of components in three main parts of the complement system, presenting in characteristic but different ways
Alternate and terminal pathways present with infection
Deficiencies of classical pathway components characteristically present as lupus-like systemic immune complex disease
What are cryoglobulins?
Immunoglobulin molecules which reversibly precipitate out of solution at temperatures under 37 degrees celsius
In what conditions are cryoglobulins seen?
Livedo reticularis Raynaud's Peripheral cyanosis Purpura/vasculitis Glomerulonephritis Neuropathy Arthralgia Thrombosis Haemorrhage
How are connective tissue diseases diagnosed?
History
Examination
Relevant investigations
Laboratory investigations