Lymphocytes

Question	Answer
What are the central cells of adaptive immunity?	Lymphocytes bearing antigen receptors, which are responsible for its characteristic properties of diversity, specificity, and memory.
What proportion of circulating leukocytes do lymphocytes constitute? Contrastingly, what proportion of lymph cells do they constitute?	Lymphocytes make up 20-40% of the body's leukocytes, and 99% of the cells in lymph.
Roughly how many lymphocytes are there in the body?	~10^12 (a trillion)
What are the three broad subdivisions of lymphocytic cells?	B lymphocytes, T lymphocytes, and natural killer cells.
Which lymphocytes are involved in cell-mediated immunity?	T lymphocytes
Which lymphocytes are involved in humoral immunity?	B lymphocytes
Which two cell types can B cells mature into?	Plasma and memory B cells.
Which four cell types can naive T lymphocytes mature into?	T regulatory, T cytotoxic, T helper, and memory T cells.
What is the main function of plasma B cells?	To secrete antibody.
What is the main function of B memory cells?	To react quickly and specifically to an antigen next time it is encountered by the memory B cells.
When do naive B and T lymphocytes mature?	When they are stimulated by interaction with antigen.
Where are most lymphocytes activated?	In the lymph nodes, where they proliferate and mature into effector cells.
Describe an unprimed/naive T/B cell.	Small (~6μm diameter), motile, nonphagocytic cells which cannot be differentiated from one another morphologically. Their cytoplasm forms a barely discernible ring around their nuclei, they have densely packed chromatin, few mitochondria, and a poorly developed endoplasmic reticulum and Golgi apparatus. The naive lymphocyte is generally thought to have a short life span.
In their inactivated state, which cell cycle phase do B and T lymphocytes remain in?	G0.
What do naive T/B cells differentiate into initially, when first interacting with antigen?	Lymphoblasts, 15μm diameter cells with a higher cytoplasm-to-nucleus ratio and more organellar complexity than small lymphocytes.
Memory cells look like small lymphocytes. How can they be distinguished?	By the presence or absence of certain molecules on their cell membranes.
How can B and T cells be distinguished down an electron microscope?	B cells look 'hairy' because of their IgD receptors, whereas T cells look much smoother.
What is the main mechanism for differentiating B and T cells, as well as differentiating the many cells in the different lineages and maturational stages of lymphocytes?	Recognition by monoclonal antibodies. All of the monoclonal antibodies (those specific for a single epitope of an antigen) that react wit a particular membrane molecule are grouped together as a cluster of differentiation (CD). Around 250 CD markers have been described for human lymphocytes.
Which type of T lymphocyte is a CD4+ lymphocyte?	A T-helper lymphocyte.
Which type of T lymphocyte is a CD8+ lymphocyte?	A T-cytotoxic lymphocyte. Variably, natural killer cells can possess CD8+ antigenic epitopes.
Which type of lymphocyte possesses CD21 antigenic epitopes on its cell membrane?	B lymphocytes

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	Created by sophietevans about 10 years ago