After all, a nail is sharp, and the inside of the nose is sensitive. Putting a foreign object deep into your nasal cavity isn't particularly comfortable, and it can be certainly painful when the performer is learning to do the trick. However, another obstacle -- sneezing -- can be harder to overcome.
Osteoclasts are the bone cell that destroys bone. This allows bone  remodeling, and allows the skeletal system to act as a reservoir  for minerals to maintain blood mineral â¦ levels. Bone cells that are involved in reabsorption and breakdown of the  bone matrix are referred to as osteoclasts.
There are two types of MHC molecules, MHC class 1 and 2. All nucleated cells express MHC 1 molecules when infected (including T cells). Cytotoxic T (CD8) cells only recognise MHC 1 molecules. When cells are infected with viruses, they express MHC 1 molecules.This allows cytotoxic T cells to destroy infected cells. MHC class 2 molecules are only expressed by professional antigen presenting cells (APCs) such as macrophages.