B Cells and the Adaptive Immune System

Describe B cells.

-antibody producing -humoral immunity -made in bone marrow -usually need T cells for full activation -they can become antigen-presenting cells -they can develop into plasma cells, which make most of our antibodies.

What are some characteristics of memory B cells?

-express antigen receptor on the surface. -responds quickly to antigen stimulation. -Make IgG, other antibody classes after stimulation.

Define lymphocyte.

A form of small leukocyte (white blood cell) with a single round nucleus, occurring especially in the lymphatic system.

What is the function of B1 cells?

It's almost like an innate version: doesn't have the same memory as B2 cells. Not as diverse. They have more IgM. -large numbers of similar antigen receptors. -they target bacterial carbohydrates.

Define specificity.

V(D)J recombination creates specific binding affinity for certain antigens.

What are the lymphocyte-based cells in the adaptive immune system?

-B cells -CD4+ T cells -CD8+ T cells -Regulatory cells

Where are the interaction points between the innate and the adaptive immune system?

-Dendritic cells and macrophages from the innate system can present antigens to B and T cells in the adaptive system. -Complement proteins from macrophages (innate) can bind and activate B cells (adaptive).

How is the adaptive immune system activated?

-Each B cell has a different antibody that can bind to different antigens. When they bind to an antigen, they expand. The variable region binds to the antigen, which activates the transmembrane domain. -Thymus needs large, repeating antigen. There's no memory in this, and the interaction is weak. -Thymus-dependent responses need interaction with a T cell and has stronger memory and interaction.

What are the two defining characteristics of adaptive immunity?

-Memory -Specificity

What is the function of B2 cells?

A "normal" B cell. They are diverse, and have strong memory. They have more IgG. -T cell help

What is an effector B cell?

Also known as plasma cells. They secrete antibodies.

Describe B cell activation (T-dependent).

B cells receive the first signal from antigen contact through IgAlpha. They then get an activation from a T cell through CD40/CD40L interaction.

Describe B cell activation (T-independent).

B cells receive the first signal from the antigen through binding through IgAlpha and IgBeta. The second signal is CD21 and CD19, which can come from complement or antibodies.

What are plasma cells?

Basically antibody factories.

Define "memory."

Certain immune cells are dedicated to memory. They wait for the same infection to appear again. Memory cells allow for a much faster response the second time an organism is exposed to a pathogen.

True of false: T cells and B cells originate from different sources.

False. They both originate from stem cells, specifically, from lymphocytes.

How long do memory cells last?

For years, even decades. They retain their specificity and immediately activate and proliferate upon encountering their complementary antigen.

Define humoral immunity.

Humoral immunity is the aspect of immunity that is mediated by macromolecules (as opposed to cells) found in extracellular fluids such as secreted antibodies, complement proteins, and certain antimicrobial peptides.

What are naive B cells?

Inactivated B cells.

What is the antibody location difference on memory cells and plasma cells?

Memory cells: antibodies found on outside of the cell. Plasma cells: they produce and release antibodies.

What happens post-infection?

Most immune cells die, but some of them are transformed into memory cells.

What is the timeline of innate and adaptive response?

Secondary, or adaptive, response peaks 7-14 days after initial infection. The primary, or innate, response is quicker.

Is B cell activation thymus-independent?

Sometimes. Repeating antigen binds multiple antigen receptors. B cells also engage other receptors, like TLRs and complement.

Describe the interaction between a T cell and a B cell.

T and B cells form a synapse and interact through CD40/CD40L interaction.

Describe the B cell antigen receptor.

The antibody molecule is bound to the cell surface. It directly binds the whole antigen.

What happens for thymus-dependent B cell activation?

The antigens are smaller. Only the antigen receptors needs to be bound, unlike thymus-independent activation, which requires TLRs and other receptors. The B cell presents an antigen-class II MHC (as a result of antigen binding) to the helper T cell. The helper T cell reads the presence of the antigen and provides the second signal.

What do receptor complexes do? What are some receptor complexes?

The help send signals into the cell. They are usually transmembrane, or they are on the membrane. -CD21 (complement receptor) -CD19 -IgAlpha/Beta

Describe the role of B cells in the adaptive immune system.

They are mainly involved with antibody production. They can develop into plasma cells, which produce the most antibodies. They can develop into either plasma or memory cells, and are made in the bone marrow. The can present antigens to T cells.

What do memory B cells do?

They remain in the organism after the infection has ended, and wait for it to show up again.

True of false: DNA rearrangement happens during development and diversification of T and B cells from their parent stem cell.

True

What is clonal expansion? What are the effects of it?

When immune cells encounter their antigen and then start to proliferate and differentiate. Proliferation is making more cells, differentiation is separating into memory and effector cells. The more cells there are, the more effectively an organism can fight a pathogen.

What happens during clonal selection?

You start off with a small number of different specific cells. One of them is activated, so that one proliferates. This reduces in effector cells which fight the infection, and memory cells that protect against future infection.