James Goding; Week 11 MED1011; Pathology
Neutrophils are activated when endocytic vacuole contains bacteria, K enters vacuole and proteases are released, bacteria is digested. Innate system also has NET that has DNA, histones and anti-microbial peptides. Innate system captures and presents to the adaptive system. There is a two-signal model to lymphocyte activation. Signal 1 is the antigen and 2 is co-stimulation or T cell help. Signal of antigen alone leads to tolerance, apoptosis or anergy (cell survives but is long term unresponsive). Co-stimulation by APC to B cells is by CD28.
10 toll receptors exist, phylogenically ancient, part of innate immunity and recognise pathogen associated molecular patterns. These cause anti-bacterial responses. They also turn on co-stimulatory molecules on dendritic cells.
Antibodies are important for recovery from bacterial infections and prevention of viral infections. They neutralise bacteria by binding to it. Fc portion allows opsonisation. They can also neutralise viruses. MHC presents infection in infected cell to T cells. CD4 see MHCII, CD8 see MHCI.
Bacteria can have antibiotic resistance, capsules can prevent phagocytosis, waxy envelope can prevent intracellular destruction, can have resistance to intracellular destruction (TB) and also have antigenic variation. Viruses can have antigenic variation, recombination, suppression of apoptosis, suppression of antigen presentation, expression of cytokines or decoy receptors for signalling molecules. Protozoa can have antigenic variation or sequestration away from the immune system.
Factors determining infection are microbial factors (dose and virulence), host factors (route of infection, host susceptibility genes, immune status), medical interventions