Table 1.

Immune Mechanisms described in Transplantation Tolerance.

Mechanism
Clonal Deletion	CD4+ cells
	CD8+ T cells
	B cells
Clonal Exhaustion	Apoptosis
Clonal Anergy	Systemic donor hypo-reactivity
Specific unresponsiveness	CD4+ cells transfer from tolerant hosts
Regulatory T cells	Naïve Treg
	Activated Treg Ts1, Ts 2, Highly potent Th1-like Th2 like
Chimeric Donor Derived haemopoietic and lymphoid cells	Regulatory
	Effect Clonal silencing
Graft Factors	Alloantigen mass
	Inhibitory factors secretion
Donor Dendritic cells	Depletion/graft adaptation
	Stimulation of regulatory cells
	Failure to stimulate effector cells
Immune ignorance	–
Antibodies to Class II MHC	Blocks CD4+T cell activation and effectors
Excessive Immune activation	Dependent on grafts antigen presenting cells