Two newly diagnosed HLA class II-deficient patients identified by rapid vector-based complementation analysis reveal discoordinate invariant chain expression levels.
BACKGROUND
Primary immunodeficiencies represent the 'molecular Achilles' heels' of human immunity. Detailed analyses of primary immunodeficiencies extend our knowledge of pivotal immunological processes, lead to novel diagnostic algorithms and shorten the time to diagnosis.


METHODS
Clinical/immunological phenotypes of 2 unrelated patients from Austria with combined immunodeficiency were determined. Leukocyte subpopulations of these patients, their parents and healthy controls were analyzed by flow cytometry. Patient-derived Epstein-Barr virus (EBV)-transformed B cell lines were established and complemented by candidate cDNAs. Suspected mutations were confirmed by DNA sequencing.


RESULTS
Phenotyping revealed a lack of constitutive human leukocyte antigen (HLA) class II expression on antigen-presenting cells of both patients, compatible with MHC class II deficiency. Rapid vector-based complementation analysis of the patients' B cells identified HLA class II transactivator (CIITA) deficiency in patient VIP1 and regulatory factor X (RFX)AP deficiency in patient VIP2. CIITA deficiency was caused by a homozygous p.Glu381X mutation. RFXAP deficiency resulted from a homozygous p.Ser123ThrfsX15 mutation, not described in the Middle European population so far. Of note, HLA class II-associated invariant chain (Ii) expression levels were significantly reduced in VIP1 and 3 additional EBV-transformed B cell lines of CIITA-deficient patients but normal in EBV-transformed B cells from VIP2. In addition, peripheral blood B cells from the parents of VIP1 showed significantly reduced HLA-DR and -DP expression levels compared to healthy controls.


CONCLUSIONS
Analysis of patients' intracellular Ii and their parents' surface HLA class II expression levels might help to identify CIITA-deficient patients already during initial phenotyping.
Schmetterer
Klaus G
KG
Institute of Immunology, Center for Physiology, Pathophysiology and Immunology, Medical University of Vienna, Vienna, Austria.
Seidel
Markus G
MG
Körmöczi
Ulrike
U
Rottal
Arno
A
Schwarz
Klaus
K
Matthes-Martin
Susanne
S
Steinberger
Peter
P
Pickl
Winfried F
WF
D000328:Adult; D000361:Agammaglobulinemia; D000944:Antigens, Differentiation, B-Lymphocyte / Q000096:biosynthesis* / Q000235:genetics; D017252:CD3 Complex / Q000276:immunology; D015496:CD4-Positive T-Lymphocytes / Q000378:metabolism* / Q000473:pathology; D002460:Cell Line; D049109:Cell Proliferation; D004252:DNA Mutational Analysis; D005260:Female; D000949:Histocompatibility Antigens Class II / Q000096:biosynthesis* / Q000235:genetics; D006801:Humans; D007153:Immunologic Deficiency Syndromes / Q000235:genetics* / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology; D007223:Infant; D008231:Lymphopenia; D008297:Male; D008875:Middle Aged; D009154:Mutation / Q000235:genetics; D009687:Nuclear Proteins / Q000235:genetics*; D018089:Superantigens / Q000276:immunology; D015534:Trans-Activators / Q000235:genetics*; D014157:Transcription Factors / Q000235:genetics*
D000944:Antigens, Differentiation, B-Lymphocyte; D017252:CD3 Complex; D000949:Histocompatibility Antigens Class II; C083728:MHC class II transactivator protein; D009687:Nuclear Proteins; C413004:RFXAP protein, human; D018089:Superantigens; D015534:Trans-Activators; D014157:Transcription Factors; C045084:invariant chain