24.9
Vacunas
Descripción general
La vacunación es la administración de material antigénico de patógenos para conferir inmunidad contra un microorganismo específico…
- [Narradora] La vacunación,
la administración de una vacuna,
el material antigénico de patógenos,
prepara al cuerpo para futuras infecciones
vía patógenos específicos.
Cuando una vacuna es administrada por primera vez,
una célula inmune presentadora de antígeno, o APC,
tal como una célula dendrítica,
engulle al antígeno de la vacuna, lo degrada,
y presenta piezas del antígeno en su superficie.
Las APCs después activan a las células T ayudadoras, o Th,
que activan a los linfocitos T citotóxicos, o CTLs,
también conocidos como células T destructoras y células B.
Una vez activados, los CTLs son capaces de detectar
células infectadas, unirse a las células y liberar químicos
que matan a las células junto con los patógenos albergados.
Posterior a la activación por las Th,
las células B se dividen en células plasma y B de memoria.
Las células plasma hacen anticuerpos
que se unen a los antígenos introducidos por la vacuna
para destruir y eliminarlos del cuerpo.
Después de la infección simulada inducida por la vacuna
se ha aclarado, algunas células T son convertidas en
células de memoria que pueden fácilmente dividirse y crecer
cuando sea que una reexposición al mismo patógeno o
a sus antígenos ocurra en el futuro.
Las células de memoria y los anticuerpos generados
vía vacunas contra un patógeno específico
permanecen en el cuerpo por meses o años a la vez,
dependiendo de la vacuna.
Cuando un individuo es infectado por el mismo patógeno
o antígeno contra el cual fueron vacunados,
las células de memoria reconocerán al antígeno
y pueden dividirse rápidamente para producir
una respuesta inmune más rápida.
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Q1: How do antigen-presenting cells activate the immune system after vaccination?
Antigen-presenting cells (APCs) such as dendritic cells engulf vaccine antigens, degrade them, and display antigen pieces on their surface bound to MHC molecules. APCs then migrate to lymph nodes where they stimulate naive helper T cells and cytotoxic T cells. This activation triggers cell-mediated immune responses that prepare the body to recognize and eliminate the pathogen if encountered later.
Q2: What is the difference between plasma cells and memory B cells after vaccination?
After activation by helper T cells, B cells differentiate into two types. Plasma cells immediately produce antibodies specific to vaccine antigens that bind to and destroy pathogens. Memory B cells persist in the body for months or years, enabling rapid antibody production upon future exposure to the same pathogen, providing long-term immunity.
Q3: How do memory cells provide faster immune protection during reinfection?
Memory T cells and B cells generated during vaccination recognize antigens from previously encountered pathogens. Upon reexposure, these memory cells divide rapidly and mount a quicker, more efficient immune response than the initial vaccination. This accelerated response prevents or reduces disease severity when the actual pathogen is encountered.
Q4: What role do cytotoxic T lymphocytes play in vaccine-induced immunity?
Cytotoxic T lymphocytes (CTLs), also called killer T cells, are activated by helper T cells after vaccination. CTLs detect infected cells, bind to them, and release chemicals that kill the cells along with harbored pathogens. This cell-mediated response is crucial for eliminating virus-infected cells and preventing pathogen spread.
Q5: How does herd immunity protect unvaccinated individuals in a community?
Herd immunity occurs when a high percentage of the population is vaccinated against a pathogen, preventing its transmission throughout the community. Even unvaccinated individuals, including those too young or immunocompromised to receive vaccines, have reduced infection risk because the pathogen cannot find sufficient susceptible hosts to propagate.
Q6: Why does the influenza vaccine need to be reformulated annually?
The influenza virus evolves at an exceptionally rapid rate, with new viral strains emerging frequently. Because existing vaccines target specific viral strains, a new vaccine must be developed each year to match the currently circulating influenza variants and provide effective protection against infection.
Q7: What types of antigens are used in different vaccine formulations?
Vaccines contain antigens derived from specific pathogens in different forms. Inactive vaccines contain intact but non-replicating antigens, while subunit vaccines contain only pathogen fragments. Attenuated vaccines use live weakened pathogens that stimulate immune responses without causing severe disease, and many vaccines include adjuvants to enhance immune responses.