Page 172 - 84 human physiolofy part-1

Chapter 9

IMMUNE RESPONSE PATHWAYS

The innate response starts first, and it is reinforced by the more specific acquired response. The
two pathways are interconnected, so cooperation and communication is essential.

INFLAMMATION

What happens when bacteria invade? If the first line of defense fails, bacteria can reach the
extracellular fluid. There they usually cause an inflammatory response. This response coats antigens on
the bacterial surface, with antibodies. Then in return the antibodies will ingest the antigens with
phagocytic cells. This is characterized by a red, swollen warm area that is tender or painful. In addition
to the nonspecific inflammatory response, lymphocytes attracted to the area produce antibodies keyed
to the specific type of bacteria. If the infection continues it will produce a fever.

• What causes a fever?

During an infection macrophages may release cytokines (see glossary), such as interleukin-1, that
travel to the hypothalamus and induce a change in the thermostat setting. When the thermostat is raised
to a new normal temperature, the previous body temperature now registers as too cold. To increase the
temperature to the new level, our body shunts blood away from the skin (leaving it feeling cold and
clammy), the heart rate increases, and we shiver to generate heat until we reach the new set point. The
hypothalamus may subsequently lower the thermostat, in which case we suddenly feel hot and start to
sweat as our body attempts to cool off. A person may cycle between chills and sweats during the course
of an infection. While a fever can be dangerous if it gets too high, or if a patient is weak or has heart
trouble, there is some evidence suggesting that the body may overcome an infection faster if a fever is
allowed to run its course.

INTRACELLULAR DEFENSE

What happens when virus's invade the body?

First they encounter an extracellular phase just like the bacteria did. In the early stages of a viral
infection, innate immune responses and antibodies can help control the invasion of the virus. Once the
virus enters the body's host cells cytotoxic T lymphocytes are the main defense against intracellular
viruses. These cells look for infected host cells, then destroy them.

ACQUIRED IMMUNITY: ANTIGEN-SPECIFIC RESPONSES

Acquired immunity responses are antigen-specific responses in which the body recognizes a
foreign substance and selectively reacts to it. This is mediated primarily by lymphocytes. Acquired
immunity overlaps with the process of innate immunity. Acquired immunity can be subdivided into
active immunity and passive immunity.

Active Immunity occurs when the body is exposed to a pathogen and produces its own antibodies.
Active immunity is active because it is the "activation" of your immune system. Active immunity can
occur naturally, when a pathogen invades the body, or artificially, like when we are given vaccinations

172 | Human Physiology