KIN 140 Section 3 Dr Mike Walsh
Any microorganism, foreign protein, or abnormal cell that activates the immune system is
called an antigen (antibody generator).
When a disease-causing agent attacks the body, it encounters 3 major lines of defense.
First line of defense is non-specific and is part of the innate immune system and consists
of the following:
1) physical barriers (skin, mucous membranes, cilia)
2) chemical barriers (saliva, sweat,sebum, tears, lysozyme, digestive enzymes,
3) resident bioflora (beneficial microbes living on our skin and in our bodies that help
block infection by disease-causing microbes).
The second line of defense is also part of the non-specific, innate immune system and
includes the following:
1) non-specific immune cells (eosinophils, basophils, neutrophils, macrophages)
2) chemical mediators (interleukin-1, interferon, complement)
The third line of defense is part of the adaptive or acquired immune system. This line of
defense provides specific, long-term protection against microbes. The third line of
defense includes the following:
1) T-cells (helper and cytotoxic)
2) B-cells (memory and plasma cells)
3) antibodies 2
A. Immunity Cells
The cellular defense mechanisms consist of various white blood cells produced by bone
Macrophages: very large white blood cells that devour pathogens and worn out cells
Neutrophils: another white blood cell type that ingests pathogens
Natural killer cells: destroy pathogens, cells infected with pathogens, and cancerous cells.
Large: cells like natural killer cells are part of the innate system. They kill lots of
pathogens or cells with pathogens inside and cancerous cells.
Small: T cells (helper T cells, killer T cells, suppressor T cells, and memory T
cells) and B cells (produce antibodies and retain memory). Both are part
of our adaptive immune system.
B cells (produce antibodies and retain memory)
B. The Immune Response (Fig 13-1)
Avirus (for example) enters the blood stream. The following 10 steps are a general
overview of a successful defense.
1. Scavenger cells such as neutrophils recognize the virus as foreign and destroy some of
the viruses. This response is rapid but short-lived.
2. Resident antibodies with enough specificity will attack the virus.
3. Macrophages also devour the invading viruses and signal helper T cells. (first 3 steps
are identifying the antigen)
4. Macrophages, the clever scavengers that they are, take surface proteins of the virus a
put them on their cell membrane. This macrophage antigen activates T helper cells.
5. Helper T cells multiply and activate B and killer T cells production in the spleen and
6. B cells multiply and in our lymph nodes (this is why your lymph nodes swell) end up
doing two things:
1. many transform into plasma cells that produce antibodies that work as a ‘lock and
key’antibody production (2,000 per second per cell).
2. and some become memory B cells (see 10). 3
7. Antibodies bind to the virus and will destroy them or make them more vulnerable to
destruction by macrophages.
8. Killer T cells destroy both viruses and the body’s own cells that have been infected
with the virus.
9. T suppressor cells monitor antibody production and down-regulate it when the
destruction of viruses is succeeding.
10. Some T and B cells become memory cells able to launch a quicker and more
successful attack against future invasion of the same antigen. Furthermore, circulating
antibodies are now present.
Many of the asymptomatic symptoms produced early in the infection are due to the
immune response. Lymp