Structure and Function of Lymphocytes: Topic 1 Flashcards
what are lymphocytes?
a type of WBC found primarily in lymphatic organs such as the spleen, tonsils, and lymph nodes
what are the three main types of lymphocytes?
T cells
B cells
natural kill cells (NK cells)
where do lymphocytes arise from?
All arise from hematopoetic stem cells within the bone marrow
however, each type of lymphocyte matures in a different fashion and has its own function within the body
T cells mature in the thymus while B and NK cells mature in the bone marrow
what are T cells and B cells part of?
our adaptive immune system
T cells: cell-mediated immunity
B cells: humoral-mediated immunity
what are NK cells part of?
our innate immune system
they respond to and kill virus-infected cells as well as tumor cells
To which parts of the immune system do T cells, B cells, and NK cells belong?
T and B cells are part of adaptive immunity, and NK cells are part of innate immunity
do B and T cells look different?
normal, unstimulated B and T lymphocytes look identical
to tell them apart, special studies that detect cell surface markers are required
what do B and T cell lymphocytes look like?
slightly larger than RBCs
round with a large nucleus and very little cytoplasm
chromatin has a clumpy and smudgy appearance
what do NK cells look like?
they are larger than unstimulated T and B cells
more abundant cytoplasm
less condensed chromatin pattern
what are plasma cells?
specialized B cells that make tons of antibodies
what do plasma cells look like?
there’s lots of protein production happening from all the antibodies being made so they have a unique appearance
the nucleus is eccentric (off-center**), pushed to the side by a big glob of pale-staining rough endoplasmic reticulum
clumps of chromatin arranged around periphery of nucleus
Where do T cells form and mature?
T cells are formed in the bone marrow and mature in the thymus.
what happens when you have an underdeveloped or absent thymus?
results in recurrent viral and fungal infections due to the lack of mature T cells available to fight infections.
like in DiGeroge syndrome
how are T cells differentiated from one another?
by the various receptors on their cell surface
what do helper T cells do?
also called CD4+ cells
- assist in the activation of macrophages
- help with the maturation of B cells into antibody-secreting plasma cells
what do CD8+ Cells do?
cytotoxic T cells
they secrete molecules that help destroy whatever cell they are bound to
what do CD25+ T cells do?
help modulate immune responses
what are the types of T cells?
helper T cells
CD8+ T cells
CD25+ cells
what are T cells implicated in?
type IV hypersensitivity reactions and in acute and chronic organ rejection
where do B cells form and mature?
B cells also arise from lymphoid stem cells within the bone marrow – but unlike T cells, B cells stay in the marrow to mature
what are the roles of B cells?
they are able to secrete cytokines (signaling molecules)
they can differentiate into plasma cells, which make antibodies
what are memory B cells?
upon coming into contact with an antigen for the second time, can mount a swift response to the infection
this is the idea behind vaccines! if we can “prime” the body to recognize an infection by using part of a virus or bacteria, then when we encounter the pathogen our body will be able to quickly and efficiently fight off the infection
what is agammaglobulinemia?
not being able to form mature B cells
what is multiple myeloma?
creating an overabundance of plasma cells
a malignancy in which plasma cells proliferate in the bone marrow
what is x-linked agammaglobulinemia?
not being able to form mature B cells
characterized by a complete lack of immunoglobulin (antibodies) due to the inability of B cells to mature and differentiate into plasma cells
B cells can differentiate into which two types of cells?
memory B cells and plasma cells
what do NK cells do?
they are pre-programmed to recognize virus-infected cells and tumor cells
destroy target cells via the exocytosis of cytoplasmic granules containing two key enzymes, perforin and granzyme
where do NK cells come from?
lymphoid stem cells
just like T cells and B cells
what is perforin?
it creates pores, or holes, within an infected cell’s membrane that allow granzymes to pass into the cytoplasm of the infected cell.
it’s inside the cytoplasmic granules of NK cells
what are granzymes?
serine proteases that, once inside the infected cell, initiate apoptosis, or programmed cell death. This helps stop the progression of the virus or the tumor
granzymes enter the infected cell after perforin has created pores in the cell membrane
it’s inside the cytoplasmic granules of NK cells
what do NK cell deficiencies cause?
rare but lead to increased susceptibility to herpesvirus and papillomavirus infections.
Which two enzymes do natural killer cells use to fight virus-infected cells and tumor cells?
NK cells use perforin and granzymes to fight virus-infected cells and tumor cells
which cell marker identifies a helper T cell?
CD4
all T cells have the CD3 cell marker
which cell marker identifies a a cytotoxic T cell?
CD8
which cell marker identifies a regulatory T cell?
CD25
which cell marker identifies a NK cell?
CD56
