Haseeb Ullah

  Tolerance Tolerance in the immune system refers to a state where the immune system does not respond to specific antigens (or epitopes) even though it functions normally otherwise. This means that the immune system ignores certain substances as if they were not harmful. Typically, antigens that are present during embryonic development are identified as "self" and do not trigger an immune response. This is because self-reactive T-cell precursors are eliminated in the thymus during fetal development. Antigens encountered later, after the immune system has matured, are considered "NonSelf" and usually provoke an immune response. Although both T cells and B cells are involved in tolerance, T-cell tolerance is more crucial.   T Cell Tolerance Tell tolerance mainly occurs in the thymus during fetal development. This process, known as clonal deletion, involves the destruction of T cells that react against self-antigens (mainly self-major histocompatibility complex [

Platyhelminthes Definition Platyhelminthes (Flatworms)   Characteristics: Flattened, bilaterally symmetrical bodies.   Group: Includes both freeliving and parasitic species.   Medical Importance: Parasitic flatworms include classes like Trematoda (flukes) and Cestoda (tapeworms). Lifecycle in Humans Trematodes (Flukes) 1 . Eggs: Released in human feces or urine. 2. Larval Stages: Eggs hatch into miracidia, infecting intermediate hosts (usually snails). 3. Cercariae: Develop within snails, released into water. 4. Human Infection: Penetrate human skin or ingested. 5. Adult Stage : Migrate to organs (e.g., liver, lungs), mature into adult flukes. 6. Reproduction: Adults lay eggs, excreted from human body. Example: Schistosoma spp. Lifecycle 1. Eggs: Excreted in feces. 2. Miracidia: Hatch and infect snails. 3. Cercariae: Released from snails, penetrate human skin. 4. Schistosomula: Migrate through the bloodstream to the liver. 5. Adults:

  Nematodes (Helminths): Lifecycle in Humans, Diagnosis, and Treatment   Definition Nematodes (Roundworms)   Phylum: Nematoda   Characteristics:    Cylindrical, elongated, unsegmented bodies   Habitats:    Soil, Water, Parasitic environments (plants and animals, including humans) Lifecycle in Humans 1. Ingestion/Penetration: Ingest eggs/larvae via food, water, soil; some penetrate skin. 2. Larval Migration: Larvae move through tissues (e.g., lungs, intestines). 3. Adult Stage: Mature in specific body locations (e.g., intestines, lymphatics). 4. Reproduction : Adults reproduce; eggs excreted in feces or remain in tissues. 5. Environmental Stage : Eggs/larvae develop in environment; become infectious. Ascaris lumbricoides Example 1. Ingestion: Ingest eggs via contaminated food/water. 2. Hatching: Eggs hatch in intestines. 3. Migration: Larvae move to lungs, then throat, swallowed back to intestines. 4. Maturation: Mature into adults in intest

Toxoplasma: Its Life Cycle, Symptoms, and Prevention Life cycle   Definitive Host: Domestic cats and other felines.   Intermediate Hosts : Humans and other mammals. Cycle in Cats: 1. Cats ingest cysts (e.g., from raw meat like mice). 2. Cysts release bradyzoites in the small intestine. 3. Bradyzoites infect mucosal cells and differentiate into gametocytes. 4. Gametocytes fuse to form oocysts. 5. Oocysts are excreted in cat feces. Human Infection: 1. Ingestion of cysts via:     Undercooked meat     Accidental contact with cat feces 2. Cysts rupture in the small intestine, releasing forms that invade the gut wall. 3. Forms differentiate into tachyzoites (rapidly multiplying trophozoites). 4. Tachyzoites infect various tissues (e.g., brain, muscle). 5. Tachyzoites transform into bradyzoites, forming tissue cysts. Transmission:   Contaminated soil with cat feces ingested inadvertently.   Consumption of undercooked meat from animals grazing in contam

  Leishmania donovani: Life Cycle, Pathogenesis, Treatment Prevention and Diagnosis   Leishmania donovani: The Causative Agent of Kalaazar (Visceral Leishmaniasis) Lifecycle   Reservoir Hosts: Various mammals (e.g., dogs, foxes, rodents).   Vector: Female sandflies.    Require blood meals for egg maturation.    Ingest macrophages containing amastigotes when feeding on an infected host. Inside the Sandfly: 1. Amastigotes transform into promastigotes in the gut. 2. Promastigotes multiply and migrate to the pharynx and proboscis. 3. This process takes about 10 days. Transmission to Humans: 1. Sandfly bites human, injecting promastigotes. 2. Promastigotes are engulfed by macrophages. 3. Inside macrophages, promastigotes transform back into amastigotes. Within the Human Host: 1. Amastigotes evade destruction by preventing vacuolelysosome fusion. 2. Infect other macrophages and reticuloendothelial cells. Cycle Completion:   Another sandfly ingests