LESSONS FROM GENE KNOCKOUTS

The authors describe the technique for the application of homologous r ecombination in embryonic stem cells, which is now widely used to engi neer mice which carry specific knockouts of genes. A summary is given of some of the knowledge of the pathogenesis of and resistance to infe ctions with parasites, bacteria, or viruses which has accumulated duri ng recent years, based on the investigation of knockout mice. Special emphasis is placed on knockout animals which la ck components of the c ytokine network, lack genes which are critical for the correct present ation of antigens or are deficient in different immune cell subsets, i n addition, a brief explanation is offered of the possibilities for in ducing targeted deletions or mutations in genes of livestock species ( e.g., by nuclear transfer or by mutagenesis using the alkylating agent N-ethyl-N-nitrosourea) which could lead to the breeding of animals wh ich are resistant to infectious diseases in the future.