Extra

CD79a

pan-b cell marker that has high degree of specificity for the identification of b-lineage. CD79a is expressed initially in cytoplasm before appearing on the membrane as surface heavy chain expression is acquired.

normal expression and function CD79a associates with CD79b and the immunoglobulin chains of the b-cell receptor. together these chains mediate the signalling of the b-cell receptor however each is expressed slightly differently - CD79a is more reliable lineage-specific marker than CD79b which may have more variable expression. expression is acquired during early b-lymphocyte formation - initially in cytoplasm before appearing on the membrane of more mature cells and persisting until plasma cell differentiation.

diagnostic role

• reliable marker of b-lymphocyte lineage with relatively low levels of aberrant expression
• CD79a should be considered more specific than CD19 or CD20 although it may rarely be expressed on other cell types.
• in all expression in cytoplasm is acquired at an early stage of b-lineage commitment pro-b differentiation
• expression is on the cell surface at later differentiation as surface heavy chains are acquired.
• in myeloma about half of cases will express this marker strongly with further proportion having weak expression.

other relevant information CD79a expression is recognised on some aml and t-all cases so caution should be exercised particularly where other features are atypical. like CD19 expression of CD79a is more often associated with aml that has t 8;21 translocation though less common .

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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