Hypersensitivity reactions are immune responses that can cause tissue damage. There are four types of hypersensitivity reactions, with a possible fifth type. Type I hypersensitivity is mediated by pre-formed IgE bound to mast cells, leading to mast cell degranulation and immediate reactions such as anaphylaxis and atopic allergies. Type II hypersensitivity involves antibodies directed towards antigens on cell surfaces, leading to cell injury and reactions such as transfusion reactions and autoimmune haemolytic anaemia. Type III hypersensitivity involves the formation of immune complexes, leading to reactions such as post-streptococcal glomerulonephritis and SLE. Type IV hypersensitivity is cell-mediated, involving T lymphocytes and causing granulomatous conditions or direct cytotoxicity, such as contact dermatitis and the Mantoux test. There is also a possible fifth type, caused by stimulatory autoantibodies in autoimmune conditions like Graves’ disease. It is important to distinguish between these types of hypersensitivity reactions based on their clinical presentation and histological features.

Understanding the Causes of Haemolytic Disease of the Newborn

Haemolytic disease of the newborn is a condition that occurs when a mother’s antibodies attack her infant’s red blood cells. This can happen due to a variety of reasons, including rhesus factor incompatibility and immune complex deposition.

Rhesus factor incompatibility occurs when a rhesus-negative mother has previously been sensitised to the rhesus antigen, usually from a previous rhesus-positive pregnancy or blood transfusion. In subsequent pregnancies, IgG antibodies made by the mother due to previous exposure can cross the placenta and attack the infant’s red blood cells.

Immune complex deposition, which is a type III hypersensitivity reaction, can also cause haemolysis. This occurs when immune complexes deposit in tissues and trigger an inflammatory response. Examples of conditions that can cause this type of reaction include systemic lupus erythematosus and farmer’s lung.

It’s important to note that haemolysis in haemolytic disease of the newborn is triggered by maternal IgG antibodies, not IgE antibodies. Anaphylactic reactions, which are triggered by IgE antibodies, are a separate issue.

Understanding the causes of haemolytic disease of the newborn is crucial for proper diagnosis and treatment. Pregnant women should be screened for rhesus factor incompatibility and other potential risk factors to prevent this condition from occurring.

Diagnostic Tests for Blood Transfusion Reactions

Blood transfusion reactions can be life-threatening if not diagnosed and treated promptly. Several diagnostic tests are available to identify the cause of haemolysis and diagnose an ABO incompatibility transfusion reaction. Here are some of the commonly used tests:

Direct Antiglobulin Test (Coombs Test)
This test is used to identify whether red blood cells have antibodies attached to their surface. It is useful in diagnosing the cause of haemolysis in ABO incompatibility following transfusion, haemolytic disease of the newborn, drug-induced anaemia, and other autoimmune conditions that cause the destruction of red blood cells.

Erythrocyte Sedimentation Rate (ESR)
ESR measures the sedimentation of erythrocytes in a tall, thin tube of blood. Although it is not a useful test to establish the cause of haemolysis and diagnose an ABO incompatibility transfusion reaction, it can be used to diagnose infection, cancers, and inflammatory disease.

Indirect Antiglobulin Test
This test is an in vitro test for antibody-antigen reactions prior to blood transfusion. It can detect very low concentrations of antibodies in a patient’s plasma to ensure that donor blood will be compatible.

Schirmer’s Test
This test is used to diagnose keratoconjunctivitis sicca (dry eyes).

White Cell Count
Obtaining a white cell count is not a useful test in diagnosing an ABO incompatibility transfusion reaction. Although the patient may have fever and chills, it is likely secondary to a blood transfusion reaction rather than an acute infective process.

Hypersensitivity Reactions: Types and Examples

Hypersensitivity reactions are immune responses that occur when the body reacts to a harmless substance as if it were harmful. There are four types of hypersensitivity reactions, each with different mechanisms and clinical presentations.

Type I hypersensitivity reaction is an immediate reaction mediated by IgE in response to an environmental antigen. Mast cell and basophil degranulation result in the release of histamine, causing symptoms such as allergic rhinitis and systemic urticaria.

Type II hypersensitivity reaction is an antibody-mediated reaction that results in cellular injury. Examples include incompatible blood transfusions, haemolytic disease of the newborn, and autoimmune haemolytic anaemias.

Type III hypersensitivity reaction is an immune complex-mediated reaction. Immune complexes are lattices of antibody and antigen that trigger an inflammatory response when not cleared from the circulation. Extrinsic allergic alveolitis, or bird fancier’s lung, is an example of this type of reaction.

Type IV hypersensitivity reaction is a delayed reaction involving T helper cells that become activated upon contact with an antigen. Cytokine release from sensitised T-cells leads to macrophage-induced phagocytosis. This type of reaction is seen in contact dermatitis and some cases of extrinsic allergic alveolitis.

Anaphylaxis is a type I-mediated hypersensitivity reaction that results in rapid respiratory and circulatory compromise. Skin and mucosal changes, such as rash with wheal and angio-oedema, are also present.

In summary, hypersensitivity reactions can have different mechanisms and clinical presentations. Understanding the type of reaction is important for proper diagnosis and management.

Diagnostic Tests for Coeliac Disease

Coeliac disease is a condition that affects the small intestine and is caused by an intolerance to gluten. There are several diagnostic tests available to help establish a diagnosis of coeliac disease. The first line test is the IgA tissue transglutaminase (tTGA) antibody serology. A positive test indicates that further testing, such as endoscopy and biopsy, is needed for confirmation.

Before testing, it is important to confirm that the patient has been consuming gluten-containing foods regularly for at least six weeks. HLA testing is not a first line test and should only be carried out in secondary care.

If the tTGA test is unavailable or weakly positive, IgA endomysial antibody testing may be used as a second line test. Small bowel biopsy is only indicated if serology is positive or equivocal.

There is no indication for an abdominal CT scan in this scenario. The first line investigation for coeliac disease is serology, and if positive, diagnosis is confirmed or excluded by biopsy of the small bowel at endoscopy.

Comparison of Immune Cells: T Cell, Mast Cell, B Cell, Dendritic Cell, and Kupffer Cell

The immune system is composed of various types of cells that work together to protect the body from foreign invaders. Among these cells are T cells, mast cells, B cells, dendritic cells, and Kupffer cells.

T cells are characterized by their T-cell receptors (TCRs), which are composed of polypeptide a and b chains connected by disulfide bonds. Each chain of the TCR has a variable and a constant region that folds into an immunoglobulin (Ig)-like domain.

Mast cells, on the other hand, contain numerous granulocytes and secrete histamine when stimulated. They do not have TCRs.

B cells have a B-cell receptor (BCR), which is a complex of Ig-a and Ig-b (signal transducers) associated with membrane Ig molecules. The BCR has two antigen-binding sites.

Dendritic cells are resident macrophages found in the skin. They do not have TCRs.

Kupffer cells are resident macrophages found in the liver. Like dendritic cells, they do not have TCRs.

Understanding the characteristics of these immune cells is crucial in developing strategies to combat diseases and infections.

Vaccination Schedule for Infants: A Breakdown of Recommended Vaccines

The recommended vaccination schedule for infants includes several vaccines that are given at different ages. Here is a breakdown of the vaccines and when they are typically administered:

– Eight weeks: Rotavirus and 6-in-1 vaccines
– 12-14 months: MMR vaccine
– Eight weeks, 16 weeks, and one year: Pneumococcal vaccine
– Eight weeks, 16 weeks, and one year: Meningitis B vaccine
– Eight weeks: Hib/Men C vaccine (combined vaccine for Haemophilus influenzae type b and meningitis C)

It is important to follow the recommended vaccination schedule to protect infants from serious illnesses and diseases. Consult with a healthcare provider for more information and to schedule vaccinations for your child.

Treatment Options for Acute Allograft Reaction in Solid Organ Transplants

Solid organ transplants have become increasingly successful with the use of immunosuppressants, but optimizing their dosage and regimes is crucial to prevent rejection and minimize side-effects. Acute allograft reaction is a major cause of graft rejection and can be classified as T-cell mediated rejection (TCMR), antibody-mediated rejection (ABMR), or mixed rejection. Treatment is guided by the Banff grading of the biopsy, with pulsed methylprednisolone being the first-line treatment for Banff grade IA or IB TCMR. Alemtuzumab is used in patients who cannot tolerate rATG-thymoglobulin, while belatacept is used for prevention therapy against ABMR. rATG-thymoglobulin is given for Banff IB TCMR, and tacrolimus is used in triple immunosuppressant maintenance therapy.

Cell Types in the Skin: Langerhans, Eosinophil, Basophil, Melanocyte, and Merkel Cell

The skin is composed of various cell types, each with their own unique functions. Langerhans cells, originating from the bone marrow, are antigen-presenting cells found in the epidermis. They process antigens that enter the body via the epidermis and are involved in allergic dermatitis reactions. Eosinophils and basophils are rare in the epidermis, but if present, would be found in cutaneous blood vessels or the dermis and/or hypodermis. Melanocytes, on the other hand, are responsible for producing melanin, which gives skin its color. Langerhans cells lack melanin granules and are more closely related to monocytes. Finally, Merkel cells are dendritic cells found in the stratum basale and are associated with nerve fibers, likely playing an important sensory function. Understanding the different cell types in the skin can help in diagnosing and treating various skin conditions.

Overview of Immune System Cells and Proteins

The immune system is composed of various cells and proteins that work together to protect the body from foreign invaders. Here are some key components:

Lymphoid stem cells: These cells can differentiate into B lymphocytes, T lymphocytes, plasma cells, and natural killer cells.

Basophils: These cells are involved in inflammatory and allergic reactions. They contain heparin and histamine.

Myeloid stem cells: These cells can differentiate into various types of white blood cells, including monocytes, macrophages, neutrophils, basophils, eosinophils, and dendritic cells, as well as red blood cells and platelets.

CD40: This protein is found on antigen-presenting cells and is required for their activation.

Plasma cells: These cells are antibody-secreting white blood cells that originate from B cells in the bone marrow and differentiate in lymph nodes.