24.9
Aşılama
Genel bakış
Aşılama, belirli bir mikroorganizmaya karşı bağışıklık kazandırmak için patojenlerden antijenik materyalin verilmesidir. Aşılama, gerçek p…
Aşılama, patojenlerden elde edilen antijen maddelerin uygulanması vücudu belli bir patojene bağlı enfeksiyonlara karşı hazırlar. Aşı ilk yapıldığında antijen sunan bağışık bir hücre veya APC, örneğin bir dendritik hücre, antijeni aşıdan içine çeker, parçalar ve antijen parçalarını yüzeyinde sergiler. Daha sonra APC'ler T-yardımcı hücrelerini (Th) aktive eder, bu da katil T-hücreleri de denen sitotoksik T-lenfositlerini (CTL) ve B hücrelerini tetikler.
Aktifleşen CTL'ler enfekte hücreleri tespit eder, hücrelere bağlar ve salgıladığı kimyasallarla bu hücreleri ve içindeki patojenleri öldürür. Th tarafından aktivasyon sonrası, B hücreleri plazmaya ve hafıza B hücrelerine bölünür. Plazma hücreleri antikorlar üretir, bunlar aşıyla tanıtılan antijenlere bağlanıp onları yok eder ve vücuttan atar.
Aşıyla başlatılan yalancı enfeksiyon temizlendikten sonra bazı T-hücreleri hafıza hücrelerine dönüşür ve ileride aynı patojene veya antijenlerine tekrar maruz kalındığında kolayca bölünerek çoğalabilir. Belli bir patojene karşı aşıyla oluşturulan antikorlardaki hafıza hücreleri aşıya bağlı olarak vücutta aylarca veya yıllarca kalır. Kişi aşısını yaptırdığı patojen veya antijenle enfekte olduğunda hafıza hücreleri antijeni tanıyacak ve hızla bölünerek daha çabuk immün yanıt verecektir.
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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.