24.3
Respuestas inmunes humorales
Descripción general
La respuesta inmune humoral, también conocida como respuesta inmune mediada por anticuerpos, se dirige a los patógenos que circula…
- [Instructor] En la otra respuesta adaptativa inmune,
la inmunidad humoral, el sistema inmunológico se enfoca en
los patógenos en los fluidos extra-celulares
que incluyen sangre y linfa.
Los patógenos invasivos como bacterias son detectados
por leucocitos específicos llamados células B
que reconocen antígenos específicos en
superficies bacterianas.
Una vez que los células B son activadas proliferan
y se diferencian como células plasmáticas
que segregan millones de anticuerpos
que circulan a través del cuerpo
y activan varios mecanismos de defensa.
En un método, los anticuerpos que se adhieren a los
antígenos en la superficie de un patógeno pueden
desactivarlo o neutralizarlo interfiriendo con su habilidad
para infectar la célula huésped.
También pueden opsonizar o etiquetar a los patógenos
para engullición y destrucción de los fagocitos
tales como macrófagos o neutrófilos.
Finalmente, los anticuerpos pueden activar el sistema
complementario, un complejo de proteínas que mejora
la opsonización y destrucción de patógenos.
Incluso con los patógenos destruidos, algunas células B
se diferencien en células B de memoria
en vez de células plasmáticas.
Eras células B de memoria continúan produciendo
pequeñas cantidades de anticuerpos mucho después
de que pasó la infección.
Si el mismo patógeno vuelve a entrar en el cuerpo
estos anticuerpos circulantes pueden captarlo
para la destrucción inmediata.
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Q1: What are the main defense mechanisms antibodies use to destroy pathogens?
Antibodies destroy pathogens through three primary mechanisms: neutralization, opsonization, and complement system activation. Neutralization occurs when antibodies bind to pathogen surfaces and interfere with their ability to infect host cells. Opsonization tags pathogens for destruction by phagocytes like macrophages and neutrophils. The complement system, a cascade of over 30 proteins, further enhances pathogen destruction and triggers inflammatory responses.
Q2: How do B cells recognize and respond to invading pathogens?
B cells detect pathogens by recognizing specific antigens on bacterial surfaces through their B cell receptors. Upon antigen binding and receiving a second signal from helper T cells or the antigen itself, B cells become activated and form germinal centers. In these centers, B cells proliferate and differentiate into plasma cells that secrete millions of antibodies, or into memory B cells that provide long-term immunity.
Q3: What is the difference between plasma cells and memory B cells?
Plasma cells are short-lived B cells that actively secrete large quantities of genetically identical antibodies circulating throughout the bloodstream. Memory B cells are long-lived cells that produce antibodies bound to their surface and enable rapid, stronger immune responses upon reexposure to the same pathogen. Memory B cells persist long after infection clears, providing lasting immunity.
Q4: Why do patients with antibody deficiencies suffer from frequent infections?
Patients with antibody deficiencies like hypogammaglobulinemia lack sufficient antibodies to neutralize, opsonize, or activate complement against pathogens. Without adequate antibody production, pathogens circulating in blood and lymph evade destruction, leading to frequent ear, sinus, pulmonary, and gastrointestinal infections. Infections by unusual pathogens become severe, and common pathogen infections are often recurrent.
Q5: How does the humoral immune response target pathogens in body fluids?
The humoral immune response targets pathogens circulating in extracellular fluids like blood and lymph. B cells detect specific antigens on pathogen surfaces and differentiate into plasma cells that secrete antibodies. These antibodies circulate throughout the body, binding to antigens and activating defense mechanisms including neutralization, opsonization, and complement system activation.
Q6: What role do memory B cells play in secondary immune responses?
Memory B cells persist long after initial infection and continue producing small amounts of antibody. When the same pathogen reenters the body, circulating antibodies from memory B cells immediately target it for destruction, enabling faster and stronger immune responses. This mechanism provides long-term protection against reinfection by previously encountered pathogens.
Q7: How does the complement system enhance pathogen destruction?
The complement system is a sequential cascade of over 30 proteins activated by antibodies binding to antigens. These proteins opsonize pathogens for destruction by macrophages and neutrophils, induce inflammatory responses that recruit additional immune cells, and promote lysis of pathogen membranes. This multi-step process significantly amplifies the antibody-mediated immune response.