Похоже, в оригинале опечатка. Розеткообразование (rosetting)- это один из способов сортировки клеток (в данном случае, негативная сортировка иммуноденситометрическим методом) наряду с пэннингом и др. см.: Immunodensity cell separation, also referred to as erythrocyte rosetting, is a negative selection method that uses a combination of antibody-based labeling and density gradient centrifugation. With this method, antibodies are added to a whole blood sample, labeling the unwanted cells and cross-linking them to red blood cells. This results in the formation of complexes called immunorosettes that are much denser than the mononuclear cells being isolated. During centrifugation, the unwanted cells pellet with the red blood cells, leaving the target cells in a layer above the density medium https://www.stemcell.com/cell-separation/methods