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Kx antigen, the McLeod phenotype, and chronic granulomatous disease: further studies
Insights
X-linked chronic granulomatous disease (CGD) can be classified into two types based on Kx antigen deficiency. Type I affects only leukocytes, while Type II impacts both leukocytes and red blood cells.
Area of Science:
- Immunology
- Genetics
- Hematology
Background:
- X-linked chronic granulomatous disease (CGD) is a primary immunodeficiency.
- Kx antigen is typically expressed on leukocytes and red blood cells.
- The McLeod phenotype is associated with X-linked CGD.
Purpose of the Study:
- To investigate the expression of Kx antigen in patients with X-linked CGD.
- To differentiate subtypes of X-linked CGD based on Kx antigen deficiency patterns.
- To explore the genetic basis of Kx antigen expression.
Main Methods:
- Analysis of Kx antigen expression on leukocytes and red blood cells.
- Phenotypic characterization of red blood cells, including morphology and antigen activity.
- Genetic analysis of the X1k gene and its variants.
Main Results:
- Nine unrelated boys with X-linked CGD were studied.
- Leukocytes of all nine boys lacked Kx antigen.
- Three of these cases also showed Kx antigen deficiency on red cells, presenting the McLeod phenotype and abnormal red cell morphology.
- Type II CGD red cells exhibited enhanced i antigen activity, indicative of hemopoietic stress.
Conclusions:
- X-linked CGD can be categorized into two types: Type I (leukocyte-specific Kx deficiency) and Type II (Kx deficiency in both leukocytes and red cells).
- The McLeod phenotype is associated with Type II X-linked CGD.
- The X1k gene and its variants (X2k, X3k, X4k) regulate Kx antigen expression, explaining the observed phenotypes.
Abstract:
Leukocytes of nine unrelated boys with X-linked chronic granulomatous disease lack Kx antigen. In three of these cases, the red cells also lack Kx and have the McLeod phenotype and abnormal morphology. X-linked chronic granulomatous disease CGD can thus be separated into two types. Type I cases have an antigenic deficiency that is restricted to the phagocytic leukocytes while in type II, the deficiency involves both leukocytes and red cells. Red cells of type II CGD patients have enhanced i antigen activity suggesting that they are under hemopoietic stress. Normal Kx synthesis is directed by an X-linked gene named X1k. Three variants, X2k, X3k, and X4k order the different permutations of leukocyte and red cell Kx antigen production that have been recognized.