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Revision as of 10:55, 18 May 2023

tdt

tdt terminal deoxynucleotidyl transferase is expressed in the cell nucleus; detection therefore requires permeabilised cells. expression is expected in acute lymphoblastic leukaemias but is commonly also found in acute myeloid leukaemia. tdt is also strongly expressed by early haematogones and can help distinguish them from mature b cells; expression is lost as haematogones mature

what is its normal function and expression tdt acts during the v d j rearrangement of heavy chain of the t-cell receptor or b-cell receptor gene segments required for the formation of mature b and t cells in thymus or marrow. expression of tdt in normal cells is restricted to immature b-cells in bone marrow. in the t-lymphocyte lineage it is expressed by pre-t lymphoid cells and cortical thymocytes. in regenerative marrows tdt is consistently expressed on regenerative b lymphocytes haematogones which may represent a large proportion of cells in some cases particularly in children .

what is its diagnostic role the most useful attribute of tdt is its loss of expression by mature cells. *tdt is expressed by haematogones becoming lost as they mature *tdt is consistently expressed by acute lymphoblastic leukaemia 95 *tdt may be weakly expressed by burkitt lymphoma but is most often absent mature b-cell lymphomas should not express tdt although it is rarely described *tdt is expressed infrequently in aml mainly on less differentiated forms and those related to mds around 20

summary tables

expression by acute leukaemias and by haematogones hi pro-b all hi early pre-b all hi pre-b all poss b all hi pro-t all hi mature-t all mod aml hi haemato-gones

may be secondary or more primitive forms

expression by b-lymphoproliferative disorders rare cll rare pll rare mcl rare fl rare hcl rare hclv rare mzl rare lpl rare pcs

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-A pan B-cell marker with good specificity for the identification of B-lineage. CD79a is expressed initially in cytoplasm of early B cells before appearing on the membrane at the time heavy chains of immunoglobulin become expressed.
+tdt
+tdt terminal deoxynucleotidyl transferase is expressed in the cell nucleus; detection therefore requires permeabilised cells. expression is expected in acute lymphoblastic leukaemias but is commonly also found in acute myeloid leukaemia. tdt is also strongly expressed by early haematogones and can help distinguish them from mature b cells; expression is lost as haematogones mature
-normal expression and function
+what is its normal function and expression   tdt acts during the v d j rearrangement of heavy chain of the t-cell receptor or b-cell receptor gene segments required for the formation of mature b and t cells in thymus or marrow. expression of tdt in normal cells is restricted to immature b-cells in bone marrow. in the t-lymphocyte lineage it is expressed by pre-t lymphoid cells and cortical thymocytes. in regenerative marrows tdt is consistently expressed on regenerative b lymphocytes haematogones which may represent a large proportion of cells in some cases particularly in children .
-CD79a associates with CD79b and the immunoglobulin chains forming the B-cell receptor. These chains mediate intracellular signalling. However the two chains are expressed slightly differently - CD79a is a more lineage-specific marker than CD79b which often has more variable expression. Expression is acquired at a very early stage of B-lymphocyte formation - initially in cytoplasm, then appearing on the membrane of mature cells and persisting until plasma cell differentiation when it is progressively lost.
+what is its diagnostic role   the most useful attribute of tdt is its loss of expression by mature cells. *tdt is expressed by haematogones becoming lost as they mature *tdt is consistently expressed by acute lymphoblastic leukaemia 95 *tdt may be weakly expressed by burkitt lymphoma but is most often absent mature b-cell lymphomas should not express tdt although it is rarely described *tdt is expressed infrequently in aml mainly on less differentiated forms and those related to mds around 20
-diagnostic role
+summary tables
-*CD79A is a reliable marker of B-lymphocyte lineage with low levels of aberrant expression; it is more specific than CD19 or CD20 although it may rarely be expressed on other cell types.
-*in ALL expression of CD79A in cytoplasm is acquired at an early stage of B-lineage commitment while expression is on the cell surface occurs at later differentiation at the time surface heavy chains are acquired.
-*in myeloma about half of cases will express CD79A strongly, but a further proportion have weak expression.
+expression by acute leukaemias and by haematogones
+hi  pro-b all
+hi  early pre-b all
+hi  pre-b all
+poss  b all
+hi  pro-t all
+hi  mature-t all
+mod  aml
+hi  haemato-gones
+*  may be secondary or more primitive forms
-other relevant information
+expression by b-lymphoproliferative disorders
+rare cll
-CD79a expression is recognised on some cases of AML and T-ALL so caution should be exercised if other features are atypical. Like CD19 the expression of CD79a by AML is more often associated with the t(8;21) translocation.
+rare  pll
+rare  mcl
+rare  fl
+rare  hcl
-----  summary tables  1. expression by acute leukaemias and by haematogones file freq  pro-b all   hi  early pre-b all   hi  pre-b all   hi  early b all   rare  pro-t all   rare  mature-t all   poss  aml   hi  haemato-gones  link flow cytometry key CD79a cytoplasmic together with CD19 and CD22 can be used in to indicate b-lineage in pro-all and remains cytoplasmic until the b-all stage 2. expression by b-lymphoproliferative disorders file hi frame  cll *  hi  pll**   hi  mcl   hi  fl  *  hi  hcl**   hi  hclv   hi  mzl   hi  lpl   freq  pcs
+rare  hclv
+rare  mzl
+rare  lpl
+rare  pcs

Extra: Difference between revisions

From haematologyetc.co.uk

Revision as of 10:55, 18 May 2023