**Acknowledgements**

The authors are thankful to the Department of Zoology, University of Calcutta for their support and research scholars of the Immunology Laboratory for their generous help for completing this research work. We also like to acknowledge Department of Science and Technology, Govt. of India (SB/SO/HS-106/2013, dated November 21, 2014), Department of Atomic Energy -BRNS: (37(1)/14/54/2014- BRNS/1740 dated October 28, 2014), West Bengal Department of Biotechnology (22(Sanc)/BT (Estt)/RD-20/2013 dated January 07, 2015) for their financial support to carry out these works. Fellowship support from Council of Scientific and Industrial Research (CSIR), India (for SM, SG) and University Grants Commission (UGC), India is also hereby acknowledged.
