What does it mean that tissue type should match? (Tissue compatibility)

Tissue type is a term used to describe a collection of similar cells in each person that are important for immune recognition of foreign substances such as viruses, bacteria products, damaged cells etc. Tissue type varies from individual to individual and they define each one of us immunologically. ‘Matching’ tissue can be defined as trying to find tissue’s that are most similar in appearance, and this be done by using different laboratory techniques. The importance of matching tissue has become somewhat less used with modern immunosuppression (reduction of the immune system) but is still used in kidney transplants.