Infectious Diseases

Innate: Fast responses immediately upon encountering pathogen . Adaptive: Slower responses as more time is needed to develop specific responses ___________________________________ Innate: non-specific as the same response is triggered for all types of pathogens . Adaptive: different responses triggered against specific types of pathogens by recognition of specific antigens ___________________________________ Innate: Has no memory cells, no difference in responses when a reinfection occurs . Adaptive: has memory cells so responses are more rapid efficient when reinfection occurs ___________________________________ Innate: involves physical and chemical barriers as well as phagocytes . Adaptive: involves lymphocytes

Passive: Antibodies directly provided to the individual . Active: Antibodies are produced by the individual

Natural: Occur from natural processes . Artificial : Occur through medical interventions

Physical - skin: physical barrier to prevent pathogens from entering & infecting cells - mucus to trap pathogens, preventing them from infecting epithelial cells - ciliated epithelial cells in trachea to sweep mucus . Chemical - HCL in stomach kills pathogens - lysozyme in saliva and tears to digest bacteria cell wall, killing bacteria

• Pathogen attaches to the membrane evaginations called the pseudopodia . • Pathogen is engulfed and ingested by the macrophage to form a phagosome. Phagosome fuses with a lysosome to form a phagolysosome . • Hydrolytic enzymes digest the pathogen and waste products released via exocytosis

Definition Cytokines: ligands / Signal protein in the immune system that can trigger inflammatory responses . Chemokines: A specific type of cytokine ___________________________________ Role Cytokine: Activate cells in the immune response like macrophages, B cells and T cells . Chemokines: Recruits immune cells like neutrophils to the site of infection

Vasodilation: - Blood vessels dilate to allow for more blood flow to site of infection - Allow for more phagocytes to engulf and digest any pathogens via phagocytosis ___________________________________ Permeability of blood capillaries increases to allow: - More movement of phagocytes to - accumulation of tissue fluid, which causes swelling - Inflammatory mediators to stimulate sensitive pain receptors causing pain at site of infection

• Dendritic cells / macrophages ingest pathogens via phagocytosis. . • Enzymes in the phagolysosome digest pathogens in short peptide fragments . • The short peptide fragments are loaded onto major histocompatibility complexes (MHC) to form peptide-MHC complexes . • The complexes are transported via secretory vesicles that fuse with the CSM of the APC to embed them . • Peptide-MHC complexes on the CSM are presented to specific T cell receptors of naive T cells

• APCs act as the bridge between the innate and adaptive immunity by carrying out antigen presentation . • Antigen presentation by macrophage and dendritic cells signal for activation of naive T lymphocytes, kickstarting a specific response by adaptive immunity

T cell receptor of naive T cell binds to complementary peptide-MHCs (major histocompatibility complex) on macrophages/ dendritic cells (APCs) . - APCs secrete cytokines to activate naive CD4+ T cells NOT naive CD8+ T cells . - Naive CD4+ T cells will then undergo clonal expansion via mitosis and differentiate into helper T cells and memory T cells . - T helper cells secrete cytokines to activate naive CD8+ T cells - naive CD8+ T cells form cytotoxic T cells and CD8+ memory T cells

When it occurs - Prior to antigen exposure, during development of naive B cells in the bone marrow. . - one V, one D and one J region In heavy chain - AND one V and one J In light chain - are randomly selected and ligated via DNA recombination. - the remaining seq are deleted . PURPOSE - Gives rise to many diff combinations of V(D)J regions - so B cells can produce a wide variety of antibodies w different 3D conf of their antigen binding sites

• Somatic hyper mutation occurs • after antigen exposure, selected clones of B cells are activated by helper T cells to undergo clonal expansion via mitosis . Somatic hyper mutation • (( During clonal expansion, )) • extensive point mutations occur at the recombined V(D)J region of the variable region of the heavy and light chain GENES . • B cells produce antibodies with slightly different specific 3D conf of antigen binding sites . • AND different affinities to antigens . Affinity maturation • antibodies w highest affinity bind the most complementarily and continue to undergo clonal expansion via mitosis , • while those w lower affinity undergo apoptosis . ALSO • Selected B cells can differentiate into plasma B cells • which can secrete antibodies w higher affinity for the same antigen (( PURPOSE OF AFFINITY MTURATION )) . OR • Selected B cells can further differentiate into memory B cells and remain in circulation for immunological memory, • enabling a stronger, faster, longer lasting secondary response

• BCR of naive B cell bind to specific antigens on the pathogen that is comp in shape . • B cell takes up pathogen via receptor-mediated endocytosis and are processed to form peptide-MHC complex, which are embedded onto the CSM for antigen presentation . • Upon antigen presentation, peptide-MHC complexes displayed on naive B cells can bind to the T cells receptors of helper T cells . • Helper T cells secrete cytokines to activate naive B cells, • causing B cells to undergo clonal expansion via mitosis . • Naive B cells then differentiate into plasma B and memory B cells

• diff gene segments at the constant region (Fc region) of the heavy chain are rearranged and ligated to the previously recombined VDJ segments . • The results in prdtn of diff classes of antibodies that evoke diff effector functions while the antigen binding sites remain specific to the same antigen

• neutralisation - Ag binding site of Ab binds to the Ag of the pathogen / toxin (that is comp in shape) - prevents pathogen/toxin from binding to host cell receptors and infecting the host cell . • opsonisation - Fab region of Ab binds to the Ag of the pathogen - Fc region of the Ab binds to the Fc receptors on phagocytes - promotes more rigorous phagocytosis . • agglutination - two Fab regions of Ab binds to two pathogens at the same time - allows clumping of pathogens and also promotes phagocytosis

• cytotoxic T cells recognise infected host cells by binding complementary T cell receptors to peptide-MHC complexes on their cell surface . • secrete perforins to create pores into the cell . • secrete granzymes through the pores to trigger apoptosis of infected cells, killing the pathogen

CD4+ T helper cells secrete cytokines which 1 - activate naive B cells to undergo clonal expansion and differentiate into plasma B cells that secrete antibodies . 2 - enhance phagocytosis by macrophages . 3 - stimulate migration of other immune cells (cytotoxic and macrophages) to the site of infection . 4 - help naive CD8+ T cells differentiate into cytotoxic T cells