QUESTION 4
The Role of
Lymphocyte
HEMALATHA
What is lymphocyte ?
A lymphocyte is a type of white blood cell in the immune system,
including both the B andT cells of the adaptive immune system and
natural killer (NK) cells of the innate immune system.
T cell
T - cells
•
T cells mature in the thymus and contain T cell
receptors (TCRs) that allow them to bind to antigens
on MHC complexes.
•
T cells are a major component in cell-mediated
adaptive immunity because they provide a pathway
for the direct killing of pathogens.
•
There are two main types of T cells that express
either CD4 or CD8 depending on signals that occur
during T cell maturation.
Types of T cells
Helper T cells (CD4s)

Facilitate the organization of immune responses, and can bind to MHC class II.

Subtype 2 helper T cells present antigens to B cells.

Subtype 1 helper T cells produce cytokines that guide cytotoxic T cells to pathogens
and activate macrophages.
Cytotoxic T cells (CD8s)

Destroy pathogens

They
function
associated
similarly
to
with
an antigen.
natural killer
cells
by
binding to MHC class I
and releasing perforin, granzymes, and proteases to induce apoptosis in a pathogen.

They are different from NK cells because they only bind to cells that express their
specific antigen
Types of T cells
Suppressor T cells (T-reg cells)

Ability to bind to self-cells.

They have an immunosuppressive effect that inhibits cell-mediated immunity at the
end of a response

Destroys autoimmune T cells that aren’t filtered out by negative selection in the
thymus.
Memory T cells

Created after an adaptive immune response subsides, retaining the presented antigen.

They rapidly proliferate and differentiate into helper and cytotoxic T cells that are
specific to that antigen should it be detected in the body again.
B cell
B - cells
•
Produce antibodies that circulate through the
plasma.
•
Mature in bone marrow tissues and contain B
cell receptors (BCRs) that bind to antigens.
•
After antigen presentation, the naive B cells
migrate together to germinal centers within the
lymphoid tissue, where they undergo extensive
proliferation and differentiation into different
types of mature B cells.
Types of B cells
Plasma cells

Long-lived B cells that are the main source of antibodies.

They do not have the ability to proliferate and are considered
terminally-differentiated.
Plasmablasts

Plasma blasts are short-lived B cells produced early in an
infection.

Their antibodies have a weaker binding affinity than those of
plasma cells.
Types of B cells
Regulatory B cells (B reg cells)
Immunosuppressive B cells that secrete anti- inflammatory

cytokines (such as IL-10) to inhibit autoimmune lymphocytes.
Memory B cells

Dormant B cells with the same BCR as the B cell from which they differentiated.

They are specific to the antigen presented to that BCR and rapidly secrete large
amounts of antigen-specific antibodies to prevent reinfection if that antigen is
detected again.
B cells also…….
●
B cells may also function in antigen presentation
●
B cells are important to adaptive immune
function
●
Autoreactive B cells may cause autoimmune
disease that involves antibody-induced damage
and inflammation.
●
Certain B cells may undergo malignant
transformation into cancer cells such as
lymphoma, in which they continually divide and
form solid tumors.
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