RATIONALE: A rare case of hyper IgE syndrome (HIES) associated with prolidase Deficiency (PD)METHODS: Description of clinical presentation and review of metabolic, immunologic and genetic mechanisms.RESULTS: A 23 y old man was diagnosed as suffering from hepatosplenomegaly and anemia at age of 7 weeks. In spite of recurrent skin abscesses, recurrent bacterial pneumonias, mental and developmental retardation, facial abnormalities, patient was diagnosed as HIES only at age of 10 years. Persistent hepatosplenomegaly has been misdiagnosed. At age 23 y the diagnosis of PD has been made by the detection of dipeptiduria. The inheritance of both HIES and PD in our patient is autosomal recessive. Despite of recurrent neutropenia during infections, chemotaxis, peroxidation, adherence and bactericidal activity of neutrophils were found to be normal. Immunoglobulin levels and IgG subclasses were normal. IgE levels ranged between 1000 to 2000IU/ml. Lymphocyte subsets analyzed by flowcytometry showed borderline proportion of T lymphocytes, most of them activated (DR+), borderline CD3/CD4 ratio, mildly increased proportion of monocytes, reduced proportion of B lymphocytes and normal natural killer cells. In lymphocyte proliferation assay we found normal response to B cell mitogen (SAC) and significantly reduced response to T (PHA) & (Con -A) and T+B mitogens (PWM).CONCLUSIONS: Our patient is the first case of HIES and eosinopenia associated with PD and the second case of HIES and PD ever described. The mechanism of the association between these diseases is not well understood and further biochemical, immunological and molecular research is needed. RATIONALE: A rare case of hyper IgE syndrome (HIES) associated with prolidase Deficiency (PD) METHODS: Description of clinical presentation and review of metabolic, immunologic and genetic mechanisms. RESULTS: A 23 y old man was diagnosed as suffering from hepatosplenomegaly and anemia at age of 7 weeks. In spite of recurrent skin abscesses, recurrent bacterial pneumonias, mental and developmental retardation, facial abnormalities, patient was diagnosed as HIES only at age of 10 years. Persistent hepatosplenomegaly has been misdiagnosed. At age 23 y the diagnosis of PD has been made by the detection of dipeptiduria. The inheritance of both HIES and PD in our patient is autosomal recessive. Despite of recurrent neutropenia during infections, chemotaxis, peroxidation, adherence and bactericidal activity of neutrophils were found to be normal. Immunoglobulin levels and IgG subclasses were normal. IgE levels ranged between 1000 to 2000IU/ml. Lymphocyte subsets analyzed by flowcytometry showed borderline proportion of T lymphocytes, most of them activated (DR+), borderline CD3/CD4 ratio, mildly increased proportion of monocytes, reduced proportion of B lymphocytes and normal natural killer cells. In lymphocyte proliferation assay we found normal response to B cell mitogen (SAC) and significantly reduced response to T (PHA) & (Con -A) and T+B mitogens (PWM). CONCLUSIONS: Our patient is the first case of HIES and eosinopenia associated with PD and the second case of HIES and PD ever described. The mechanism of the association between these diseases is not well understood and further biochemical, immunological and molecular research is needed.