Each antibody molecule has four peptide chain, two short chains called light chains and two longer chains called heavy chains.

$\Rightarrow$ Hence an antibody is represented as $\mathrm{H}_{2} \mathrm{~L}_{2}$.

Different types of antibodies are produced in our body. $IgA$, $IgM$, $IgE$, $IgG$ are some of them.

As these antibodies are present In blood, the response is called humoral immune response.