IFNs administered by the oral route show a systemic effect. Oral IFN-a caused neutropenia in mice. In contrast to their i.p. administration, oral IFN-a did not result in the presence of detectable levels of IFNs in the blood. Circulating specific antibody to IFN blocked the neutropenic effects of i.p. IFN, but did not block the neutropenic effects of the oral IFNs (2). Therefore, we examined the expression of antiviral MxA message, a type 1 IFN-specific induced signal, as a sensitive marker for type 1 IFN interaction with lymphoid cells in the gut-associated lymphoid tissue (GALT) using semi-quantitative RT-PCR on splenocytes from mice and PMNC from man after IFN-a ingestion. Both mice and man demonstrated inducible levels of Mx mRNA after ingesting IFN-a. Murine spleen T cells and CD8+ T cells also demonstrated upregulation of Mx mRNA. Therefore, ingested IFN-a acts via established pathways of type 1 IFN signalling (3). Elevated levels of activated T cells, mainly of the CD8+ (cytotoxic/suppressor) phenotype, are found in AD brains in contact with microglial cells (4). Interestingly, peripheral CD8+ T cells are depleted in AD patients (5). Lymphocytes bearing T helper and T cytotoxic/suppressor cell antigens are found in hippocampus and temporal cortex in AD (6,7). The data above suggest that lymphocytes are part of inflammation in AD, and potential immunomodulatory T and CD8+ T cells that contact ingested non-absorbed IFN in the GALT could migrate to the brain and decrease inflammation.