adenovirus serotypes differ in their natural tropism . the adenovirus serotypes 2 , 4 , 5 and 7 all have a natural affiliation towards lung epithelia and other respiratory tissues . in contrast , serotypes 40 and 41 have a natural affiliation towards the gastrointestinal tract . the serotypes described differ in at least capsid proteins , proteins responsible for cell binding , and proteins involved in adenovirus replication . this difference in tropism and capsid protein among serotypes has led to the many research efforts aimed at redirecting the adenovirus tropism by modification of the capsid proteins .