Immunological changes that inevitably occur with aging are related to the onset of various diseases including autoimmune diseases, immunodeficiency, as well as other age-reflecting (AR) diseases. They are becoming serious problems in the global trend of longevity. To understand the AR changes, we searched for genes whose expression profiles in the whole peripheral blood change dramatically as a function of age using the Agilent whole human genome 44K microarray. After examining two cohorts consisting of 154 healthy people between age 23 and 77, we discovered 16 transcripts strongly and reproducibly correlated with age. Analysis using a publicly available gene expression dataset for a variety of human immune cells revealed that some of these transcripts were highly expressed in specific cell types whose number and function are known to change with age. This analysis shed light on the molecular mechanism of AR immunological system changes. Because of its simplicity, the assay system is expected to be useful for understanding individual health conditions. (C) 2012 Elsevier Inc. All rights reserved.