25.27
Ações de anticorpos
Anticorpos, ou imunoglobulinas, desempenham um papel crítico no arsenal do sistema imunológico contra patógenos invasores. Produzidos por células B e…
Os anticorpos reconhecem e se ligam aos antígenos para formar complexos antígeno-anticorpo para eliminação de patógenos.
Depois de se ligar a um antígeno, o anticorpo neutraliza o patógeno obstruindo a interação do antígeno com os receptores na membrana da célula hospedeira, reduzindo a propagação da infecção.
Como cada molécula de anticorpo tem dois locais de ligação para o mesmo antígeno, ela pode reticular antígenos em diferentes moléculas patogênicas.
Como resultado, os anticorpos podem ligar diferentes moléculas antigênicas em complexos imunes grandes e insolúveis.
Quando antígenos solúveis, como toxinas, formam grandes complexos, eles precipitam para fora da solução.
Em contraste, antígenos em células bacterianas ou partículas virais que são reticuladas por anticorpos causam aglomeração ou aglutinação.
Em ambos os casos, os fagócitos capturam e engolfam facilmente esses grandes complexos imunológicos.
Quando vários anticorpos se ligam intimamente a uma célula, suas regiões tronco se alinham para permitir a ligação das proteínas do complemento, desencadeando a lise do patógeno.
Além disso, o revestimento de anticorpos e proteínas do complemento opsoniza, ou marca, patógenos para reconhecimento de fagocitos.
Esses patógenos opsonizados são facilmente agarrados por fagócitos para eliminação eficaz.
View the full transcript and gain access to JoVE Core videos
Q1: How do antibodies neutralize pathogens?
Antibodies bind to antigens on pathogens and block their interaction with host cell receptors, preventing infection. This neutralization mechanism stops pathogens from entering cells and spreading infection. Antibodies can also bind toxins like tetanus toxin, preventing their harmful effects on tissues.
Q2: What is antigen-antibody cross-linking and why does it matter?
Each antibody has two binding sites, allowing it to link different antigenic molecules together into large immune complexes. Soluble antigens form precipitates that settle out of solution, while antigens on bacterial cells or viruses clump through agglutination. These large complexes are easily captured and eliminated by phagocytes.
Q3: How do antibodies activate the complement system?
When multiple antibodies bind closely on a pathogen's surface, their stem regions align to allow complement proteins to attach. This triggers pathogen lysis and destruction. Complement activation amplifies the immune response and recruits additional immune cells to the infection site for enhanced defense.
Q4: What is opsonization and how do antibodies facilitate it?
Opsonization is the process where antibodies and complement proteins tag pathogens for recognition by immune cells. These opsonized pathogens are easily gripped and engulfed by phagocytes for effective elimination. This marking system enhances the efficiency of pathogen removal from the body.
Q5: How do antibodies contribute to inflammation?
Antibodies trigger inflammation by binding to antigens and activating the complement system, which releases inflammatory mediators. This inflammatory response recruits more immune cells to the infection site, amplifying the body's defense against pathogens. The coordinated response enhances pathogen elimination and tissue protection.
Q6: What are the main functions of antibodies in immune defense?
Antibodies recognize and bind specific antigens to neutralize pathogens, prevent infection, and form immune complexes for phagocyte removal. They activate complement proteins, opsonize pathogens for recognition, and trigger inflammation. These diverse functions make antibodies indispensable in the body's defense against bacterial and viral infections.
Q7: How do antibodies enhance phagocytosis?
Antibodies facilitate phagocytosis by acting as opsonins that mark pathogens for immune cell recognition. When antibodies coat pathogen surfaces alongside complement proteins, phagocytes recognize and engulf these tagged pathogens more efficiently. This enhanced recognition and elimination process is critical for clearing infections from the body.