Please fill out the definition of each term
1.           Antigen presentation 

2.           Antigen presenting cell (APC) 

3.           Antigen receptor 

4.           Adaptive immunity 

5.           Adjuvant 

6.           Afferent 

7.           Affinity maturation 

8.           Allele 

9.           Allelic exclusion 

10.       Anergy 

11.       Antibody 

12.       Antibody isotype(class) 

13.       Antibody isotype(class) switching -- class switch recombination 

14.       Antigen (Ag) 

15.       B cell receptor(BCR) 

16. CD4
17. CD8
18. Cell-mediated immunity
19. Chemokine
20. Chemotaxis
21. Cluster of differentiation (CD)
22. Commensal organism
23. Complement (C')
24. Complementarity determining regions (CDRs)
25. Co-receptor
26. Cytokine
27. DAMP
28. Dendritic cell
29. Effector cell
30. Effector molecule