Laboratory Diseases of the Immune System PDF

Laboratory - Diseases of the Immune System DR. RIZZALYN A. YUSOP GENERAL PATHOLOGY LABORATORY DMD 3A/3B Hemolytic Anemia a condition where red blood cells (RBCs) are destroyed faster than they can be produced. can be associated with Type II hypersensitivit...

Laboratory - Diseases of the Immune System DR. RIZZALYN A. YUSOP GENERAL PATHOLOGY LABORATORY DMD 3A/3B Hemolytic Anemia a condition where red blood cells (RBCs) are destroyed faster than they can be produced. can be associated with Type II hypersensitivity, also known as antibody-mediated hypersensitivity. Key Features of Hemolytic Anemia observed under a Microscope 1. Chewed-Up Appearance of Red Cells: In hemolytic anemia, red blood cells are often destroyed prematurely due to factors like autoimmune processes, mechanical damage, or abnormal red cell membranes. The "chewed-up" appearance refers to the presence of fragmented or abnormally shaped cells, such as schistocytes (fragmented RBCs) and spherocytes (spherical RBCs), which are hallmarks of hemolysis. Key Features of Hemolytic Anemia observed under a Microscope 2. Odd-Shaped and Fragmented Cells: These shapes result from red cells being damaged while traveling through the blood vessels or being attacked by the immune system. This is a critical diagnostic feature in conditions like microangiopathic hemolytic anemia, where RBCs are sheared as they pass through narrowed or damaged blood vessels. Key Features of Hemolytic Anemia observed under a Microscope 3. Target Cells: These are red cells with a bullseye appearance. Target cells can be seen in various conditions, including hemolytic anemias, liver disease, or certain hemoglobinopathies. Key Features of Hemolytic Anemia observed under a Microscope 4. Presence of Reticulocytes: Reticulocytes are immature red blood cells released from the bone marrow. Normally, reticulocytes make up about 0.5% to 2% of circulating RBCs. In hemolytic anemia, this percentage increases as the bone marrow works to compensate for the rapid destruction of red cells. Hashimoto's Thyroiditis associated with Type IV hypersensitivity (delayed-type hypersensitivity) and involves a combination of cell-mediated immunity and autoantibody production (Type II hypersensitivity may also contribute). Microscopic Features of Hashimoto's Thyroiditis 1. Lymphoid Aggregates: Dense clusters of lymphocytes (both B- cells and T-cells) infiltrate the thyroid gland. These lymphoid aggregates often form germinal centers, which are structures where B-cells mature and differentiate. Microscopic Features of Hashimoto's Thyroiditis 2. Destruction of Follicular Cells: Thyroid follicular cells are destroyed and replaced by inflammatory cells. Some areas may show atrophic follicles with pink-staining colloid. Microscopic Features of Hashimoto's Thyroiditis 3. Hurthle Cell Metaplasia: Thyroid follicular cells transform into Hurthle cells (enlarged cells with abundant, eosinophilic cytoplasm) due to chronic injury and inflammation. Microscopic Features of Hashimoto's Thyroiditis 4. Fibrosis: Fibrosis replaces the normal thyroid architecture, giving a lobulated appearance. This fibrotic process contributes to the thyroid gland's firmness on palpation. Microscopic Features of Hashimoto's Thyroiditis 5. Atrophic Follicles: The normal glandular tissue is significantly reduced or absent in areas of advanced disease. Microscopic Features of Hashimoto's Thyroiditis 6. Chronic Inflammatory Infiltrate: Hashimoto's thyroiditis is characterized by the infiltration of lymphocytes, plasma cells, and other immune cells. These inflammatory cells lead to destruction of the normal thyroid architecture. Microscopic Features of Hashimoto's Thyroiditis 7. Lymphoid Germinal Centers: Active germinal centers are a hallmark of Hashimoto's thyroiditis. These centers form within the thyroid tissue itself, where B-cells proliferate and mature, indicating an autoimmune process. Microscopic Features of Hashimoto's Thyroiditis 8. Destruction of the Gland: Extensive damage to thyroid follicles is observed, leading to a decrease in functional thyroid tissue over time. Microscopic Features of Hashimoto's Thyroiditis 9. Hurthle Cells: In areas attempting regeneration, Hurthle cells appear. These are large, eosinophilic cells with abundant, granular cytoplasm. They result from follicular cell transformation due to chronic inflammation. Skin with Amyloidosis, Congo Red Stain Amyloidosis is a condition characterized by the extracellular deposition of misfolded proteins, forming insoluble fibrils known as amyloid. These deposits disrupt normal tissue architecture and function. What is Congo Red Staining? Congo red is a special stain used to detect amyloid, a pathological protein that accumulates in various tissues during amyloidosis. The dye binds specifically to the β-pleated sheet structure of amyloid fibrils. Microscopic Features with Congo Red Stain: 1. Vascular Amyloid Deposits: In the dermis, amyloid accumulates primarily in the walls of blood vessels. This deposition weakens the vessel walls and may impair normal blood flow.  Microscopic Features with Congo Red Stain: 2. Congo Red Stain: Congo red stain binds specifically to amyloid fibrils, highlighting them under the microscope. Appearance under light microscopy: Amyloid appears as homogenous pink to orange-red material. Birefringence under polarized light: Amyloid deposits show an apple-green birefringence, a hallmark diagnostic feature of amyloidosis.  Microscopic Features with Congo Red Stain: 2. Congo Red Stain: Congo red stain binds specifically to amyloid fibrils, highlighting them under the microscope. Appearance under light microscopy: Amyloid appears as homogenous pink to orange-red material. Birefringence under polarized light: Amyloid deposits show an apple-green birefringence, a hallmark diagnostic feature of amyloidosis.  Why Amyloid Targets Vessel Walls: The vascular endothelium and walls provide a conducive environment for amyloid deposition because of: High exposure to circulating proteins prone to misfolding (e.g., immunoglobulin light chains in AL amyloidosis or serum amyloid A in AA amyloidosis). Structural vulnerabilities that allow for extracellular deposition. Kaposi's Sarcoma of the Skin Kaposi’s sarcoma is a vascular tumor arising from endothelial cells, associated with Human Herpesvirus-8 (HHV-8) infection. It commonly affects the skin but can involve mucous membranes, lymph nodes, and visceral organs.  What to Look for Microscopically in the Dermis: 1. Malignant Endothelial Cells: Observation: The tumor is composed of spindle-shaped and disturbed-looking endothelial cells. These cells might resemble fibroblasts under the microscope but are, in fact, malignant endothelial cells. Significance: The endothelial cells form irregular vascular structures and are a hallmark of Kaposi's Sarcoma. Diagnostic Clue: They exhibit atypical features such as nuclear pleomorphism, hyperchromasia, and abnormal mitoses.  What to Look for Microscopically in the Dermis: 2. Extravasated Red Blood Cells: Observation: Red blood cells are found outside the blood vessels in the surrounding connective tissue. Cause: The tumor's abnormal and poorly formed vascular channels are prone to leakage, allowing RBCs to escape. Clinical Correlation: This contributes to the characteristic reddish-purple lesions seen on the skin in KS.  What to Look for Microscopically in the Dermis: 3. Hemosiderin Deposition: Observation: Dark brown or black pigment is noted in the background connective tissue or within histiocytes (macrophages). Source: This pigment represents hemosiderin, an iron-storage complex derived from the breakdown of hemoglobin in extravasated RBCs. Special Stain: Prussian Blue stain can confirm the presence of hemosiderin by staining the iron deposits blue. Clinical Relevance: This is a sign of chronic blood vessel instability and hemorrhage within the tumor.  What to Look for Microscopically in the Dermis: 4. Inflammatory Infiltrate: Mixed inflammatory cells, including lymphocytes, plasma cells, and macrophages, are often present.  What to Look for Microscopically in the Dermis: 5. Characteristic Vascular Slits: Irregular, slit-like spaces filled with red blood cells are a key diagnostic feature. These spaces reflect the abnormal angiogenesis driven by the malignant endothelial cells.  What to Look for Microscopically in the Dermis: 6. Malignant cells lining the abnormal vascular spaces The lower-left insert focuses on the malignant cells lining the abnormal vascular spaces and highlights the extravasated RBCs. This confirms the disorganized nature of the vascular channels formed by the tumor. Histological Features of Kaposi's Sarcoma: Spindle cells: Malignant endothelial cells. Slit-like vascular spaces: Poorly formed vascular channels containing RBCs. Hemosiderin deposits: Evidence of prior RBC degradation. Inflammatory infiltrate: Lymphocytes, plasma cells, and macrophages are commonly present. HHV-8 positivity: Confirmatory with immunohistochemical staining END...