Immunology: B and T-Cell Development

If an Immature B-cell will react with a: 1. No self-reaction 2. Multivalent self-molecule 3. Soluble self-molecule 4. Low affinity non-cross-linking self-molecule What will happen?

1. Migration to periphery-->Mature B-cell 2. Clonal deletion or receptor editing--> Apoptosis or generation or non-auto-reactive B-cell 3. Migration to periphery -->Anergic B-cell 4. Migration to periphery--> Mature B-cell (clonally ignorant)

True or False: B-cells only undergo negative selection, while T-cells undergo both positive and negative selection.

True.

How are auto-reactive cells rescued (strong ligation of IgM by self-antigen)?

-Arrest of B-cell development and *continued light chain rearrangement*: low cell-surface IgM. -A new receptor specificity is now expressed. -If still reactive, cell will go undergo apoptosis. -If no longer self-reactive, it will migrate to periphery and mature.

B cell development:

-B-cell precursor rearranges its immunoglobulin genes in the bone marrow. -Immature B-cell bound to self-surface antigen is removed from repertoire: *negative selection in bone-marrow.* -Mature B-cell bound to foreign antigen is activated (migration of B-cells to peripheral lymphoid organs) *-Activated B-cells give rise to plasma cells and memory cells.*

Negative selection:

-Cells with strong recognition of self-MHC undergo apoptosis. -Mediated by bone marrow derived antigen-presenting cells.

Positive selection of T-cells:

-Only cells recognizing self-MHC survive. -Mediated by *cortical epithelial cells.* -MHC restricted antigen recognition. -Unsuccessful gene rearrangements may be rescued.

T-cell development:

-T-cell precursor rearranges its T-cell receptor genes in the thymus. *-Immature T-cells that recognize self-MHC receive signals for survival.* *-Those that interact strongly with self-antigen, are removed from repertoire.* -Mature T-cells encounter foreign antigens in the peripheral lymphoid organs are activated. -Activated T-cells proliferate and eliminate infection.

What is the chemokine involved in the interaction of B-cells with bone marrow stromal cells?

CXCL 12

True or False: T-cells do not originate from the same common lymphoid progenitors as B-cells.

False: *T-cells do originate from the same common lymphoid progenitors as B-cells.*

Lineage of immune cells:

Hematopoietic stem cell>Multipotent progenitor>*Common lymphocyte progenitor>Pre-B cell or Thymocyte>B-cell or T-cell.*

Where do immune cells originate?

In the bone marrow.

Thymocytes are in the ________ of the medulla.

Thymocytes are in the *cortex* of the medulla.

When B-cell fail to rearrange, cell _____ occurs.

When B-cell fail to rearrange, cell *death* occurs.

When a B-cell matures, it will express both ___ and ___ on it's surface made from alternatively spliced H-chain transcripts.

When a B-cell matures, it will express both *IgD and IgM* on it's surface made from alternatively spliced H-chain transcripts.