MONOCYTE FUNCTION IN A SEVERE COMBINED IMMUNODEFICIENT PATIENT WITH ADONOR SPLICE-SITE MUTATION IN THE JAK3 GENE

Janus kinase-3 (Jak3) is a nonreceptor tyrosine kinase functionally co upled to cytokine receptors which share a ''common'' gamma chain (gamm a c). Mutations in gamma c and Jak3 genes have been identified in X-li nked and autosomal severe combined immune deficiency (SCID), respectiv ely. Jak3 is expressed and activated in myelomonocytic cells, The pres ent study was designed to define the structural alteration responsible for lack of Jak3 in a patient with autosomal SCID and to characterize monocyte function in the absence of this signal transduction element, as well as to establish the whole exon-intron structure. Polymerase c hain reaction analysis, performed with primers designed on exon sequen ces, identified 20 exons spanning approximately 15 kb. These primers, or others designed on the flanking sequences provided in the present r eport, can be used to amplify the whole gene, allowing the definition of the molecular defects in all cases, including prenatal diagnosis, i n which transcript analysis is not possible. On this basis, the deleti on transcript found at the homozygous state in patient CM, with both h is consanguineous parents being heterozygous for the deletion, was ass ociated with mutation (T to C) of a splice donor site of intron 16 tha t was also detected in his mother's DNA. Monocytes from Jak3(-) SCID s howed normal cytokine production in response to interleukin-4 (IL-4) ( release of IL-1 receptor antagonist) and IL-2 (release of tumor necros is factor-alpha and IL-8). Lipopolysaccharide-induced cytokine product ion was also normal and was blocked by IL-4 in Jak3(-) SCID monocytes. Interferon-gamma induced augmented expression of major histocompatibi lity class II in Jak3(-) SCID monocytes, These data indicate that Jak3 , expressed and activated in myelomonocytic cells, is dispensable for monocyte differentiation and responsiveness to cytokines that interact with gamma c receptors as well as to other regulatory signals. (C) 19 96 by The American Society of Hematology.