Immunology | Immune system| Immunity

LEUKEMIA is the unchecked proliferation of an abnormal clone of hematopoietic cells.Typically,leukemic cells respond poorly or inappropriately to regulatory signals,display aberrant patterns of differentiation,or even fail to differentiate.Furthermore,they sometimes supress the growth of normal lymphoid and myeloid cells.Leukemia can rise at any maturational stage of any one of the hematopoeitic lineages.Lymphocytic leukemias display many characteristics of cells of the lymphoid lineage;another broad group,myelogenous leukemias have attributes of members of the myeloid lineage.Aside from lineage,many leukemias can be classified as cute aor chronic.Some ezamples are acute lymphocytic leukemia(ALL),the most common childhood leukemia;acute myelogenous leukemia;acute myelogenous leukemia(AML),found more often in adults than in children;and chronic lymphocytic leukemia(CLL),which is rarely seen in children but is the most common form of adult leukemia in the Western world.A fourth type,chronic(CML),occurs much more often in older adults than in children.

The diagnosis of leukemia is made on the basis of two findings.One is the detection of abnormal cells in the blood-stream,and other is observation of abnormal cells in the bone marrow.Clinical experience has shown that designing the most appropriate therapy for the patient requires knowing which type of leukemia is present.In this regard,two of the important questions are: (1)What is the lineage of the abnormal cells and (2)What is their maturational stage? A variety of approaches,including cytologic examination of cell morphology and staining characteristics,immuno-phenotyping,and,in some cases,an analusis of gene rearrangements,are useful in answering these questions.One of the most powerful of these approaches is immunophenotyping,the determination of the profile of selected cell-surface markers displayed by the leukemic cell.Although leukemia-specific antigens have not yet been found,profiles of expressed surface antigens often frequently helpful in determining the maturational stages present in leukemic cell populations.For example,an abnormal cell that displays surface immunoglobin would be assigned to the B-cell lineage and its maturational stage would be that of a mature B cell.On the other hand,a cell that had cytoplasmic heavy chains,but no surface immuno-globin,would be a B-lineage leukemic cell but at the maturational stage of a pre-B cell. The most efficient and prcise technology for immunophenotyping uses flowcytometry and monoclonal antibodies.The availability of antibodies specific for each of the scores of antigens found on various types and subtypes of hematopoietic cells has made it possible to identify patterns of antigen expression that are typical of cell lineages,maturational stages,and a number of different types of leukemia.Most cancer centres are equipped with flow cytometers that are capable of performing and interpreting the multiparameter analyses necessary to provide useful profiles surface markers on tumor cell populations.Flow cytometric determination of immuno-phenotypes allows:
* Confirmation of diagnosis