Question

what are the basics of immunology?

Answer 1

The immune system is the body’s natural defence in combating organisms.
Immunology has developed rapidly over the past decade owing to the refinements made
in the molecular tests employed in this area of research. Therefore, the keen reader is
encouraged to peruse the ophthalmic and immunological literature in order to keep
abreast of the latest developments in this field.

The immune system can be thought of as having
two “lines of defence”: the first, representing a
non-specific (no memory) response to antigen
(substance to which the body regards as foreign
or potentially harmful) known as the innate
immune system; and the second, the adaptive
immune system, which displays a high degree of
memory and specificity. The innate system
represents the first line of defence to an
intruding pathogen. The response evolved is
therefore rapid, and is unable to “memorise” the
same said pathogen should the body be exposed
to it in the future. Although the cells and
molecules of the adaptive system possess slower
temporal dynamics, they possess a high degree
of specificity and evoke a more potent response
on secondary exposure to the pathogen.
The adaptive immune system frequently
incorporates cells and molecules of the innate
system in its fight against harmful pathogens.
For example, complement (molecules of the
innate system - see later) may be activated by
antibodies (molecules of the adaptive system)
thus providing a useful addition to the adaptive
system’s armamentaria.

Anything that causes an immune response is called an antigen. An antigen may be harmless, such as grass pollen, or harmful, such as the flu virus. Disease-causing antigens are called pathogens. The immune system is designed to protect the body from pathogens.

In humans, the immune system begins to develop in the embryo. The immune system starts with hematopoietic (from Greek, "blood-making") stem cells. These stem cells differentiate into the major players in the immune system (granulocytes, monocytes, and lymphocytes). These stems cells also differentiate into cells in the blood that are not involved in immune function, such as erythrocytes (red blood cells) and megakaryocytes (for blood clotting). Stem cells continue to be produced and differentiate throughout your lifetime.

The immune systems produces Billions of kinds of B-cells each making one kind of antibody receptor.
The presence of antigen leads to the proliferation and differentiation of clones that have antibody capable of binding the antigen. In the diagram the "green" antigen binds to the green antibody on a B-cell. The color code means that only this antibody receptor on the cell binds free antigen.
The "green" helper T-cell must give a stimulatory signal to allow a particular B-cell to be selected. This step allows a regulation or control of the process.
The antigen driven selection produces memory cells and plasma cells secreting antibody capable of binding the original selecting antigen with high affinity..
If antigen appears in the organism a second time, then the memory cells are already present at high levels, and produce a more rapid and much stronger immune response.