Ptb Flashcards
- recognized subset of T helper cells
- importante modulator of inflammation and CD4+ T cell recall or memory response.
- secretes IL17
- can recruit neutrophils, monocytes and CD4+ T cells producing IFN y and stimulate chemokine expression
Th17 cells
- indicated by the negatives tuberculin test —
ANERGY
Causes of anergy or negatives tuberculin test:
- malnutrition
- HIV infection
- steroid therapy
- severe TB (due to productions of inhibitory cytokines like TGF-B)
- kill cells garbo rin intracellular pathogens,
- either exhibit granzyme/perforin-mediated killing of target T cells (first step: cell membrane destroyed) or induce apoptosis (destruction of target T-cell DNA —> LYSIS)
CYTOLYTIC or CYTOTOXIC T-LYPMPHOCYTES
- like CD8 T cell
- assoc. with inc. Replication of mycobacterial rather that susceptibility to TB
- Foundation in chromosomes 2
- linked with BCG resistance gene
Nramp (natural resistance assoc. Macrophage protektahan)
TB responsed and course
TB bacilli -> alveoli -> alveolar macrophages
Can evade intracellular killing mechanism -> Get carried to lymph Nodes and other organs.
In lungs macrophages introduce antigens to T cells -> resulting in its expansion, Development of memory Tcell of which DTH cells may be a subset -> may result tuberculin positive persistence and/or long term Protection.
Inflammatory Th1 responses -> local pulmonary infiltrates and hilar Adenopathy (PRIMARY COMPLEX).
If unable to contain: cause progressive dse -> imbalance between proinflammatory and immunosuppressive effects -> military TB
Development of progression TB occurs in ___ % of affected individuals?
10%
- After adequate treatment, some bacilli persist in a dormant state.
- clinically asymptomatic
- reactivation of dormant bacilli lead to active disease
Patent TB infection
LTBD
Factors that prompte Development and Ma Inten ace of latency?
- Low concert ratio of O2
- Nutrients in chronic granulomas
- Local production of TNF - alpha and Nitric oxide
Maintaned in Latent phase:
- TNF - alpha
- IFN - Gamma
- NO
Reactivation of TB occurs at extrapulmonary site without apparently lung lessons in ___ % of affected individuals?
15%
Leads to reactivation due to depression of cell mediated immunity:
- HIV infection
- malnutrition
- disease
- Druidrider
What age is particularly susceptible to Develop TB and are at increased risk of developing disseminated dse, particularly TBM.
Under 2yrs of age
Reason: weaker innate and adaptive responses / immaturity of immune system
Congenital infection identified possible reasons for the Development of dse:
- Impaired antigen-specific CD4p T-lymphocyte responses
- Decreased capacity of Neonatal T-lymphocytes to Secrets IFN-Y, and TNF-alpha
- cytokine production leans towards a Th2 response
- Suboptimal response of CD8p T-lymphocyte.
TB source:
- exposure
- environmental factors: overcrowding, poot Ventilation
Risk factors for TB:
AEI
- Household contact with a newly diagnosed Smear + case
- depends on the infectivity, proximity and duration of contact
- Age less than 5years
- most important factor
- determined the risk of progression to disease following primary infxn
Among immunocompetent children. - infants are at greatest risk
- risk remains significant in the 2nd yr if life
- lowest in children 5-10yo.
- Immunocompromised state (severe mal., HIV)
- host immunity, major determinant of dse develop´n
- high risk
Infectivity of smear positive vs smear negative household exposure?
60 to 80%
30 to 40%
TB morbidity with Family history exposure
2.5 Times than without knowing exposure
Additional groups at high risk of exposure and infection?
- residents and employees of closed settings
- medically underserved, low income populations
- high-risk racia and ethinic minority populations
- infection drug users
- children exposed to adults with certain medical conditions.
TB transmission and portal of entry:
- airborne
- inhalation of dropped nuclei
- 5micra
- 5 to 200 inhaled bacilli
Perinatal transmission of TB occur:
- transplacentally through umbilical vein from mother with primary hematogenous TB daring pregnancy
- aspiration/ingestion of infected AF in utero/daring delivery
- inhalation of TB bacilli at or soon after delivery (most common)
TB incubation period:
3 to 12 weeks
Shorter when the inoculum is large
Primary infection
- Occurs in person without previous exposure to tubercle bacilli.
- controlled with a reactive tuberculin skin test as the only evidence of infection.
Pathogenesis
Inhalation —> scavenging noon-activated, alveolar macrophages ingest the tubercle bacilli —> if not inhibited (virulance, microbicidal ability of macrophages) —> unrestrained replication —> some macrophages carry bacilli from lung to regional (hilar and mediastinal) lymph nodes —> disseminated via lymphatics or bloodstream (kidney, meninges, epiphyseal plates of long bones, vertebrae, apical segments of the upper lobes lungs) —> infected macrophages present tuberculous antigens to T lymph —> T-lym sensitized —> produce progeny —> secrete lymphokines (IFN-y, TNF) and activates macrophages —> inc lyrics enzyme (epitheloid macrophages, langhans giant cells)
CMI and DTH both inhibit the inc in Number of bacilli