Micro algae's are used as alternative protein source in human and animal diets. Besides micro algae contain substantial amounts of proteins they also contain a high concentration of, often unique, biological and chemical substances with potential to induce beneficial and health promoting effects in humans and animals. This study was set up to evaluate the potential of these substances to improve (intestinal) health. The effect of extracts prepared from 3 monocultures of micro algae's (Chlorella vulgaris [C], Haematococcus pluvialis [H], and Spirulina platensis [S]) and a mixed culture of micro algae's (AM; a mixture of Scenedesmus sp. and Chlorella sp. ) was studied in the presence and absence of the enterotoxigenic bacterium Escherichia coli k99 strain (ETEC, [E]) as an in vitro challenge. The E.coli-k99 strain with adhesion factor F41 (41/32) was isolated from a mastitis-infected udder. Gene expression was measured in cultured intestinal porcine epithelium cells (IPECJ2 cell line) after 2 and 6 hours incubation with C, H, and S extracts, and after 6 hours with the AM extract, using “whole genome” porcine microarrays. Gene expression profiles were analysed using functional bioinformatics programs to provide insight in the biological processes induced by micro algae extracts. Overall design: IPECJ2 cells were grown in 2 cm2 wells for 7 days at 37 ºC and 5% CO2 using 1:1 DMEM/Ham’s F10 1:1 medium supplemented with 5% FCS without antibiotics. For all tests, confluent monolayers were washed twice with medium without FCS (hereafter denoted as medium) and incubated for 1 hour with this medium. Hereafter, the medium was discarded and algae extracts suspended in medium were added to wells with IPECJ2 monolayers and incubated for a period of 2 and 6 hours in the absence and presence of ETEC (±10 cfu per cell). All incubations were tested in duplicate and for each type of additive duplicate control wells containing no additive (only culture medium) were incubated for 2 and 6 hours. After incubation total RNA was extracted. RNA's extracted from replicates were pooled (biological replicates) and this pool was hybridized in duplicate (technical replicates). IPECJ2 enterocyte cell line derived from the jejunum of piglets, host-feed interaction