Polyclonal rabbit antithymocyte globulin triggers B-cell and plasma cell apoptosis by multiple pathways

Area of Science:

• Immunology
• Transplantation Medicine
• Cell Biology

Background:

• Polyclonal antithymocyte globulin (ATG) is a standard anti-T-cell therapy in solid organ transplantation.
• Previous research indicated rabbit ATG (rATG) efficacy in treating antibody-mediated renal allograft rejection, suggesting potential anti-B cell activity.

Purpose of the Study:

• To investigate the complement-independent, apoptosis-inducing properties of rabbit ATG (rATG) on various B cell populations in vitro.
• To identify potential surface targets of rATG on B cells.

Main Methods:

• In vitro assessment of rATG's apoptosis-inducing effects on naive B cells, activated B cells, and plasma cells using annexin V staining, subdiploid DNA content, caspase activation, and mitochondrial membrane potential assays.
• Competitive inhibition assays to identify rATG surface targets by blocking monoclonal antibody binding.

Main Results:

• rATG demonstrated potent in vitro apoptosis induction against naive B cells, activated B cells, and plasma cells at clinically relevant concentrations.
• rATG activity was associated with numerous B-cell surface proteins, including CD30, CD38, CD95, CD80, and HLA-DR.
• The Fc fragment of rATG contributed to its activity, and caspase- and cathepsin-dependent pathways were implicated in rATG-induced B-cell apoptosis.

Conclusions:

• Polyclonal rabbit ATG induces complement-independent apoptosis in naive, activated, and plasma B cells.
• The observed B-cell apoptosis is mediated through caspase- and cathepsin-dependent pathways.