24.9
Vaccinazioni
Panoramica
La vaccinazione è la somministrazione di materiale antigenico da agenti patogeni per conferire l'immunità contro un microrganismo specifico…
- [Istruttore] La vaccinazione, ovvero
la somministrazione di un vaccino,
il materiale antigenico derivante dai patogeni,
prepara il corpo per future infezioni
da parte di un agente patogeno specifico.
Quando un vaccino viene somministrato per la prima volta,
un antigene che presenta la cellula immunitaria o APC
come una cellula dendritica,
inghiotte l'antigene dal vaccino, lo degrada
e mostra pezzi dell'antigene sulla sua superficie.
L'APC quindi attiva cellule T-ausiiarie o Th in breve,
che innesca i T-linfociti citotossici o CTL
noto anche come cellule T killer,
e cellule B.
Una volta attivati, i CTL possono rilevare cellule infette,
si legano alle cellule e rilasciano sostanze chimiche che
uccidono le cellule insieme agli agenti patogeni ospitati.
Nella post-attivazione dalle cellule Th,
le cellule B si dividono in plasma e cellule B di memoria.
Le plasmacellule producono anticorpi che si legano
agli antigeni introdotti dal vaccino
per distruggerli ed eliminarli dal corpo.
Dopo che l'infezione fittizia indotta dal vaccino è
eliminata, alcune cellule T vengono convertite
in cellule di memoria
che possono facilmente dividersi e crescere ogni volta che
si ripresenta l'esposizione allo stesso patogeno
o i suoi antigeni in futuro.
Le cellule di memoria generati in anticorpi tramite vaccini
contro un agente patogeno specifico
rimangono nel corpo per mesi o anni ogni volta
a seconda del vaccino.
Quando una persona viene infettata
dallo stesso patogeno o antigene
contro cui sono stati vaccinati
le cellule di memoria riconoscono l'antigene e s dividono
rapidamente per dar una risposta immunitaria più rapida.
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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.