Positive Selection of T-cells: 

• Refers to the T cell development process in the thymus by the binding of T-cell receptors (TCRs) of mature T-cells to the self-antigens presented by Major Histocompatibility Complex (MHC) of thymocytes
• Is responsible for the maturation of thymocytes
• Results in the maturation of thymocytes into either CD8+ (cytotoxic) T-cells or CD4+ (helper) T-cells 
• Antigen presentation is minimal
• Occurs in the cortex of the thymus
• Does not have the ability to activate apoptosis
• Does not suppress autoimmune reactions
• Occurs before negative selection 

Negative Selection of T-cells: 

• Refers to the process of T cell development in thymus due to the incapability of TCRs to bind the MCH complexes of thymocytes
• Prevents the formation of self-reactive T-cells
• Results in the cell death of thymocytes 
• Occurs in the medulla of the thymus
• Has the ability to activate apoptosis following strong interactions between T-cell and self antigen
• Suppresses autoimmune reaction as it does not produce self-reacting cells
• Takes place after positive selection