Antibacterial Immunity

Question 1

Describe the immune system response against extracellular bacteria (both innate and adaptive) - Macrophage

Answer 1

Macrophage - phagocytosis and beyond (receptor mediated)

1) the microbe is recognized via the opsonization process
- opsonization can occur through the use of high affinity receptors like mannose receptors (bind to mannose), Mac-1 integral receptors (binds to microbes opsonized via complement) and scavenger receptors (binds in non-mannose specific manner - so mainly lipid binding)
- alternatively, opsonization of microbe can occur by coating the microbe with one of three things - which help the phagocyte gobble that shit up right away
* antibodies
* complement proteins
* lectin
2) once the microbe is phagocytosed the phagocyte destroys the microbe by either injecting it with a reaction oxygen species (ROS) or a reactive nitrogen intermediate (RIN)
- examples of ROS are: oxygen ions, free radicals, and peroxides
- examples or RIN are: nitric oxide
3) once the antigen is processed, it is present to T-cells
4) after the presentation, pro inflammatory cytokines (IL-1, Il-6, TNF-a) are released to induce inflammation and increase chemotaxis

Question 2

Describe the immune system response against extracellular bacteria (both innate and adaptive) -neutrophils

Answer 2

also phagocytes; however, they are the first responder and eventually die and create pus. they kill microbes in same manner as macrophages (ROS/RIN) but also kill them w/o ROS using defense’s, myeloperoxidases, and neutrophil extracellular traps (NETS)

Question 3

Describe the immune system response against extracellular bacteria (both innate and adaptive) -complement

Answer 3

has 3 roles:

1) serves as opsonin
2) serves as chemokine (recruits and activates leukocytes to the site of inflammation)
3) forms the membrane attack complex and mediates the lysis of the microbe

Question 4

Describe the immune system response against extracellular bacteria (both innate and adaptive) - B-cell

Answer 4

1) production of antibodies:
- neutralization
- opsonization
- memory
2) b cells express MHC II for presentation to T-cells
3) bacterial products can directly activate B and T cells independently

Question 5

Describe the immune system response against intracellular bacteria - innate: dendritic cells

Answer 5

1) professional antigen presenting cells (typically this is done in the lymph nodes with naive T-cells)
2) carry Ag from site of infection to lymph node
3) produce cytokines that regulate the differentiation of CD4+ T cells

Question 6

Describe the immune system response against intracellular bacteria - innate: Natural Killer cells

Answer 6

1) main function is to kill virus infected cells/tumor cells that aren’t displaying MHC I
2) secrete cytokine required for macrophage and Th1 development
- Note: activation of NK cells is regulated between signals from activation and inhibitor receptors

Question 7

Describe the immune system response against intracellular bacteria - innate: T-cells

Answer 7

1) CD4+ T cell
a) recognize MHC II
b) are called Helper T cells because they differentiate into 1 or 2 subsets to provide different assistance
- Th1 subset: promote cell mediated response by released IFN-g and TNF-a
- Th2 subset: promote antibody mediated immunity by released IL-4
2) CD8+ T cell
- recognized MHC I
- called cytotoxic T cells because they directly lyse/kill infected cells (very important for viral immunity)
- secrete cytokines such as IFN-g and TNF-a

Question 8

Describe the immune system response against intracellular bacteria - adaptive

Answer 8

1) CD4+ T cells (helper T cells)

2) CD8+ T cells (cytotoxic T cells)

Question 9

List the mechanisms pathogens use to evade host responses

Answer 9

1) extracellular pathogen mechanisms
- antigenic variation - prevents binding
- inhibition of the complement activation
- resistance to phagocytosis
- scavenging of ROS
2) not to0 sure about intracellular pathogen mechanisms - maybe same as extracellular?