[Characterization of null alleles in human histocompatibility complex antigens (HLA)]. / Charakterizace nulových alel v komplexu lidských histokompatibilních antigenu (HLA).

The widespread application of DNA techniques in medicine and biology has allowed the typing of human leukocyte antigens (HLA) at the molecular level. Comparative studies between serological and molecular biology methods have shown the existence of null alleles, which code HLA antigens with low or no cell surface expression. Null alleles are not detectable by standard serological typing methods and may be overlooked/or incorrectly assigned by available DNA methods. Although null alleles are infrequent in human populations, they should not be ignored. Errors in typing of null alleles may cause complications in the evaluation of HLA matching of donor/recipient pairs that were originally considered HLA-compatible. The detection of null alleles and their frequency in various populations requires typing of a large number of individuals by both serological and DNA-based methods. Knowledge of the haplotype(s) associated with null alleles may be helpful for their identification. For this purpose, it is necessary to perform family studies.

Identification of HLA alleles with low or no cell surface expression in the Czech population.

The presence of the A*24020102L allele is implicated in one donor from the CBMD who serologically was typed as A2; B44, B55; Cwl, Cw7. The DRB4*01030102N allele was identified in one healthy donor and in one patient with MDS during routine HLA class II DNA typing. The DRB4*01030102N allele was identified in the patient's father, who had CML, and was associated with the HLA-A3-B7-Cw7-DRB1*0701-DQB1*0303 haplotype, which is common for European populations. In order to avoid mistyping, both techniques, serology and molecular biology must be used for HLA typing, especially for cases where just one antigen appeared to be present using serological methods.