Homing of lymphocytes to the secondary lymphoid organs

dont forget to study the diagrams in the ppt - not included in flashcards

what are secondary lymphoid organs?

they are the sites for initiation of adaptive immune responses

where are B and T cells in secondary lymphoid tissues?

they reside in distinct B and T cell zones

where do pathogen-derived antigens go?

they have to be brought to the secondary lymphoid organs for recognition by rare antigen-specific T and B cells

what delivers antigens to secondary lymphoid tissues?

dendritic cells deliver antigens to T cells

free antigens delivered to B cells

how do lymphocytes enter lymph nodes and get to their distic regions

enter via specialized blood vessels called high endothelial venules (HEV) in the T cell zone

the lymphocytes are then partitioned into their regions by chemokines

what is leukocyte homing?

the process by which leukocytes are guided to lymphoid tissues

what are the 3 chemokines that are important for migration and segregation of T and B cells in secondary lymphoid tissues?

CCL21

CCL19

CXCL13

these help the migration out of blood cells and into tissues 

what is in the T cell zone?

contains a network of interdigitating dendritic cells - their processes interweave among T cells

what is in the B cell zone?

contains a network of follicular dendritic cells

what are follicular dendritic cells?

specialized cells type that capture immune complexes for recognition by B cells

immune complex = complexes of antigen, antibody, and complement

Are follicular dendritic cells leukocytes?

no

they are not derived from HSC, and do not express MHC class II

T cells exiting lymph nodes - what controls it?

chemotactic lipid

what lipid molecule is involved in T cell exiting from lymph nodes?

sphingosine 1-phosphate (S1P)

forms a concentration gradient between the efferent lymph (high conc.) and the lymphoid tissue (low conc.)

where are S1P receptors (S1PR1) expressed?

they are expressed on naive T cells and effector T cells, which respond to the S1P concentration gradient

expressed on effector cells to mediate their exit from the lymphoid tissue

How is S1PR1 regulated on antigen-activated T cells?

It is transiently down regulated on antigen activated T cells

this causes their retention in the T cell zone and their differentiation into effector cells

What is FTY720?

it is an immunosuppressive drug that inhibits immune responses by sequestering lymphocytes in the lymphoid tissue