Immunology Flashcards
Most effective public health intervention after clean drinking water
Vaccination
Impact of memory on antibody production
IgM is the first antibody against an infection followed by a delayed IgG response. However this leads to clinical manifestation of the disease. Memory helps in the production of IgG prior to IgM being produced with clinical features being absorbed
What mediates secondary antibody response
Long lived plasma cells residing in bone marrow that continually secrete antigen specific antibodies IgG
Characteristics of memory B and T cells
Memory cells are present in greater numbers than original lymphocyte. CD8+ T cells can kill antigen immediately upon stimulation and CD4+ can produce cytokines immediately (overall faster response). Memory cells also have enhanced properties of cell adhesion and chemotaxis
Vaccination vs immunisation
Immunisation is an individual developing immunity/memory to a disease, natural and induced.
Vaccination is deliberate administration of antigenic material to produce immunity to disease
Active vs passive immunity
Active immunity is protection produced by persons own immune system whereas passive immunity is protection transferred from another person or animal
What are adjuvants in immunisation
Adjuvants are a mixture of inflammatory substances required to stimulate an immune response to coadministered peptides, proteins or carbohydrates. Ex: Aluminium hydroxide
Sabin or Salk polio vaccine
Salk - Inactivated and safe however expensive and doesn’t provide herd immunity, injection route
Sabin - Oral, easy to administer however there is a risk of reversion to virulent form
Source of passive immunity
Naturally acquired from mother - transplacental transport of maternal IgG in third trimester. Breast milk, especially colostrum contains IgA important for colonisation of infant gut tract
Therapeutic - Pooled normal human immunisation, hyperimmune globulin
What are pooled normal immunoglobulins
Transfer of antibodies from an unrelated individual, previously used for protection against Hep A
What is hyperimmune globulin
Administered after specific exposure, antibodies from an individual known to have high anitbody level against specific pathogen. Ex: Rabies or snake venom anti-toxin
Are there too many vaccines to be taken?
Approx. 16 vaccines by the time you’re 18. Antigen burden today is less than 50 years ago (no smallpox vaccine, no whole cell pertussis vaccine)
Hallmarks of immune deficiency
SPUR -
Serious infection - Unresponsive to antibiotics (oral)
Persistent infection - Chronic infections
Unusual infection - Unusual site or organism
Recurring infection - Two major or one major one minor
Other features suggestive of primary immune deficiency
Weight loss, failure to thrive, severe skin rash (eczema), chronic diarrhoea, mouth ulceration, family history, unusual autoimmune disease
Types of immunodeficiency
Primary - Inherited
Secondary - Acquired
What are phagocytes
Neutrophils and Monocytes/Macrophage
Primary defect causing failure of stem cells to differentiate along myeloid lineage
Reticular dysgenesis - Most severe form of Severe Combined Immunodeficiency (SCID) causing lack of innate and adaptive immune system.
What is Kostmann’s syndrome
Myelopoiesis causing congenital form of neutropenia. Recurrent systemic or localised bacterial infections within 2 weeks after birth.
Mangement of Kostmann syndrome
Supportive - Prophylactic antibiotics or antifungals
Definitive - Stem cell transplantation or granulocyte colony stimulating factor (G-CSF)which assists neutrophil maturation
Underlying pathology of patient with recurrent infections, high neutrophil blood count with no pus formation
Leukocyte adhesion deficiency, failure to recognise markers expressed on endothelial cells
What is leukocyte adhesion deficiency
Genetic defect in leukocyte integrins (CD18). Results in failure of neutrophil adhesion and migration. Leads to marked leukocytosis and localized bacterial infection that are difficult to detect
Types of PRR
PRR - Pathogen Recognition Receptor
Toll like receptor, scavenger and lectin receptor
What are opsonins
Molecules that act as binding enhancers for the process of phagocytosis. Ex: Complement protein C3b, IgG and C-reactive protein (CRP)
Indirect recognition by phagocytes
Phagocytes have receptors -
Fc receptors for antibodies bound to antigen
CR-1; Complement receptor 1 that bind to complement fragments bound to antigen
What can be defects in phagocyte function
Can be a defect in opsonisation molecules or receptors expressed on phagocytes
Disease causing deficiency of intracellular killing mechanism of phagocytes
Chronic granulomatous disease, failure of phagocyte killing mechanism. They can’t form reactive oxygen compound (ROS/RNS) due to defective phagocyte NADPH oxidase used to kill certain ingested pathogens.
Commonest deficiency in chronic granulomatous disease
Deficiency of p47phox component of NADPH oxidase
Features of chronic granulomatous disease
Recurrent deep bacterial and fungal infection
Failure to thrive
Lymphadenopathy, hepatosplenomegaly
Granuloma formation
Lab test for chronic granulomatous disease
Nitroblue tetrazolium test (NBT)
Patients are fed E.coli with dye sensitive to hydrogen peroxide. If this is produced by neutrophils, it changes colour
Treatment of chronic granulomatous disease
Supportive -
Prophylactic antibiotics and antifungals
Definitive -
Stem cell transplant, gene therapy
Host response to infection with mycobacterium such as TB
These are intracellular pathogens and infect macrophages. These infected macrophage are stimulated to produce interleukin 12 (IL-12) which induces Th1 cell proliferation and secretion on INF-gamma. This feeds back onto neutrophils and macrophages to stimulate production of TNF. NADPH oxidase is stimulated to activate the oxidative pathways.
Decfects in the IL12 : INFgamma axis are associated with
Susceptibility to intracellular bacteria
How can oxidative function of phagocytes be assessed
NItroblue Tetrazolium Test (NBT)
NBT test in congenital neutropenia
Absent due to few/no neutrophils
Life of a T-lymphocyte
T-lymphocytes arise from haematopoetic stem cells in the bone marrow. They are exported as immature cells to the thymus where they mature. They proliferate and mature and reside in secondary lymphoid follicles and lymph nodes.
CD4+ T lymphoctyes function
Immunoregulatory function -
Provide co-stimulatory signals to naive B cells and activation of CD8+ T lymphocytes.
Recognise peptides on MHC Class II molecules (APC cells only)
Produce cytokines
Function of CD8+ T lymphocytes
Specialised cytotoxic cells that kill by -
Formation of pore - perforin
Triggering apoptosis
Secrete cytokines - Interferon-Gamma
Recognise peptides in association with MHC Class I
What cells do B cells arise from
Haematopoetic stem cells
Example of haematopoetic stem cells disease
Reticular dysgenesis, corrected with bone marrow transplant
Example of disease of lymphoid precursors
Severe combined immunodeficiency
Failure of production of T and B lymphocytes from lymphoid progenitor cells
Clinical phenotype of SCID
Failure to thrive, SPUR, persistent diarrhoea, unusual skin disease, family history of early infant death
What is hypogammaglobulinaemia
Reduction in all types of gamma globulins, including antibodies that help fight infection. May be congenital or due to medication
Most common form of severe combined immunodeficiency (SCID)
X-linked SCID, mutation of IL-2 receptors. Results in inability of T cell and NK cell development as well as production of immature B cells
What IL is important to T cell development and what can it’s deficiency cause
IL-2, hence IL-2 receptor deficiency such as in X linked SCID, T lymphoctye numbers are low
Clinical phenotype of severe combined immunodeficiency
Low T lymphocyte numbers
Normal or increased B cells
Poorly developed lymphoid tissue and thymus
Treatment of SCID
Prophylactic - Avoid infections, prophylactic antibiotics and antifungals. Antibody replacement with intravenous immunoglobulins
Definitive - Stem cell transplant from sibling for HLA (or) stem cell transplant
How are T lymphocytes formed
By thymopoiesis, thymocytes are haematopoietic stem cells that differentiate into mature T lymphocytes.
How can DiGeorge syndrome lead to immunodeficiency
Developmental defect of 3/4th pharyngeal pouch causing failure of thymic development. This leads to T-cell deficiency.
Blood count in DiGeorge syndrome
Absent or decreased T cells
Normal or increased B cells -
Poor antibody response to pathogens
Normal NK cells
Management of DiGeorge syndrome
Correct metabolic/cardiac abnormality
Prophylactic antibiotics
Early and aggressive treatment of infection
Immunoglobulin replacement
Investigating T lymphocyte deficiencies
First line -
White cell count and differential, serum immunoglobulins, quantification of lymphocyte sub populations
Second line -
Functional test of T cell activation and proliferation
Additional tests of lymphocyte lineage
HIV test
What test is essential in T lymphocyte deficiency
HIV test
What infections are less common in B cell deficiency
Viral infections