Clinical Immunology Overview and use of the Laboratory

This lecture will cover • What the immunology lab measures • How they are measured • Why they are measured – (You will have other lectures expanding on this)

Immune System Cells Antibodies T-cells B cells Macrophages Neutrophils Prevent infection Complement

Components of the immune system are measured for a variety of reasons: • Their amounts can vary with infections • Abnormal components can be present with certain diseases • Immunological components can be deficient Questions • Are the components of the immune system present in normal concentrations? • Do these components function normally? • Are there known abnormal immunological components present? e. g. autoantibodies, paraproteins

Immune System Cells Antibodies T-cells B cells Macrophages Neutrophils Prevent infection Complement

Immunoglobulin concentrations in serum Normal ranges vary with age • Ig. G 6 -16 g/L • Ig. A 0. 8 -2. 8 g/L • Ig. M 0. 5 -1. 9 g/L • Ig. D 0. 1 g/L • Ig. E 0. 0001 g/L

Antibodies Total levels of Ig G, A, M autoantibodies Allergen specific Ig. E Specific antimicrobial antibodies

Measurement of Ig. G, A and M concentrations - Nephelometry • A fixed amount of antibody specific to the immunoglobulin of interest is mixed with the patient sample (serum) • Light is directed onto the reaction chamber • Light is scattered by the presence of antibody-antigen complexes • The amount of light scatter is detected

Small amount of protein. No large complexes: little light scattering

Large amount of protein. Large complexes: light scattering

Very large amount of protein. Small complexes: Little light scattering

Light Scattering Protein concentration

Abnormal immunoglobulins • Monoclonal / paraproteins • Immunoglobulin components – light chains in serum or urine (BJP) Protein electrophoresis • Separating serum proteins by charge to look for abnormalities

Autoantibodies • Many different autoantibodies have been found. – Each binds to a specific self antigen • May be found at low levels in healthy people. – Not always associated with disease • Most important are of Ig. G class – But Ig. A and Ig. M in some cases

Autoantibodies • May be pathological – i. e. the antibody causes the disease • More often found in association with disease – Eg cellular attack on an organ releases neoantigens to which antibodies develop – Indirect measure of disease state or progression

Methods for measuring autoantibodies • Indirect Immunoflourescence • ELISA • Line blot

+ Tissue section on microscope slide Antibodies in Patient Sample Antibodies bind to proteins on tissue section Fluorescently labelled antibody to human immunoglobulin Fluorescence Microscope Indirect Immunoflourescence

Section of stomach tissue Gastric parietal cells stained due to presence of autoantibody

ELISA

Line blot Recombinant Antigens fixed on a cellulose strip

Measurement of allergen specific Ig. E • Commonly known as RAST Radio. Allergo. Sorbent. Test – (Misnomer as radioactivity not used)

Ig. E levels in serum are very low • • • Ig. G 8. 0 g/L Ig. A 2. 0 g/L Ig. M 1. 0 g/L Ig. D 0. 1 g/L Ig. E 0. 0001 g/L

To detect one allergen specific Ig. E requires a very sensitive method

Immune System Cells Antibodies T-cells B cells Macrophages Neutrophils Prevent infection Complement

ALTERNATIVE pathway (AP) Classical pathway (CP) Antibody mediated C 5 convertase (AP) C 5 convertase (CP) Terminal pathway Lysis of bacteria

Complement measurement • Complement components C 3 & C 4 • Complement control proteins C 1 esterase inhibitor • Nephelometry as for immunoglobins • Complement functionality • Haemolytic assay – if all the components of the pathways are present lysis of red blood cells occurs

Immune System Cells Antibodies T-cells B cells Macrophages Neutrophils Prevent infection Complement

Lymphocytes

Distinguished by their cell surface markers (cluster of differentiation markers or CD) Detected by fluorescently labelled monoclonal antibodies to these CD markers

Lymphocytes • T cells CD 3+ – CD 4 lymphocytes are CD 3+ and CD 4+ “T helper” – CD 8 lymphocytes are CD 3+ and CD 8+ “cytotoxic T cells” • B cells CD 19+

Flow Cytometry • Cells can be differentiated by there size and granularity • Whole blood (or fractions thereof) can be incubated with fluorescently labelled monoclonal antibody to cell surface markers • Different cell types are detected by their different surface (CD) markers

Flow Cytometry Principle

Granularity Granulocytes CD 4 CD 8 Size CD 3 Monocytes Lymphocytes CD 3 CD 8

Functional tests • Lymphocyte activation – In response to mitogens – In response to antigens • Neutrophil activation

When are Immunology tests useful?

Are Immunology tests ever urgent? NO Not in the sense of say potassium (which can kill you) BUT Occasionally rapid testing is required to make an early diagnosis so that treatment can be instigated.

Circumstances when rapid testing can be helpful 1. Autoimmune renal disease – Rapidly progressive renal disease – When Goodpasture’s syndrome (anti GBM disease) or vasculitis is suspected • Anti GBM and ANCA should be measured 2. Suspected primary immune deficiency – Severe combined immune deficiency • Lymphocytes subpopulations should be measured

Measurement of Total Ig. G, Ig. A and Ig. M concentrations

Non specifically in RA, SLE autoimmune liver disease etc Increased production Infection Myeloma (monoclonal) Primary Decreased production Immunodeficiency Secondary

Allergy

Specific Ig. E testing • May contribute to the diagnosis of allergy • But only in conjunction with a careful history • A positive s. Ig. E does not always mean clinical sensitivity to an allergen • A negative s. Ig. E does not exclude allergy • Allergy is a clinical diagnosis

Clinical significance of Autoantibodies : • Presence or absence may not rule a disease in or out • Key is understanding the clinical significance of antibodies for diseases – • We use clinical sensitivity and specificity Clinical sensitivity = % of patients with given disease who have positive antibody Clinical specificity = % of healthy people who don’t have the antibody

Anti-Nuclear Antibodies (ANA) • Homogeneous ANA pattern consistent with anti-double stranded DNA Ab in SLE • Speckled ANA pattern to Anti Ro (SS-A)/ Anti La (SSB) in Sjogren’s Syndrome • ANA pattern consistent with Anti Scl 70 in Systemic Scleroderma • Centromere ANA pattern in Limited Cutaneous Scleroderma (formally CREST)

More autoantibodies • Ig. M Rheumatoid Factor present in about 80% of patients with rheumatoid arthritis and about 10% of patients without • Anti-CCP is highly specific for RA in patients with clinical features of disease (not to be used as screen) • Anti tissue transglutaminase (TTG) is highly sensitive and specific for coeliac disease • Anti intrinsic factor antibodies with anti gastric parietal cell ab specific for pernicious anaemia

Anti Neutrophil Cytoplasmic Antibody (ANCA) in renal disease P-ANCA C-ANCA - Anti MPO (ELISA) -Anti PR 3 (ELISA) - Microscopic polyangiitis> Churg Strauss > polyarteritis nodosa -Wegener’s Granulmoatosis

• Anti GBM antibodies in Goodpasture’s • Anti Mitochondrial Antibodies in Primary Biliary Cirrhosis (kidney section) Antigen is PDH (pyruvate dehydrogenase) • Anti Smooth muscle Antibody in Autoimmune Hepatitis Type 1

Use of flow cytometry • Monitoring CD 4 counts in HIV • Looking for lymphocyte defects in primary immunodeficiency

Immune System Cells Antibodies Complement T-cells B cells Igs Autoantibodies Allergen specific Ig. E RAST ANA ANCA Anti TTG RF etc

Immune System Cells Antibodies T-cells B cells Flow cytometry HIV Primary immunodeficiency Complement

The Lab is open for routine service 8 am-5 pm Outside these hours advice is available on an on-call basis Questions?