By choosing a tandem model, you will be less likely to outgrow your trailer; the extra upfront expense may be worth it in the long run. While towing level is not a factor for single axle models, level towing is a must for a tandem axle trailer. If the load is not level it can cause extra wear and tear on one set of axles, and reduce the life of your tires. The initial investment for a tandem trailer is higher than the cost for a single axle model.
The five primary classes of immunoglobulins are IgG, IgM, IgA, IgD and IgE. These are distinguished by the type of heavy chain found in the molecule.
Immunoglobulin D, also called IgD, is an uncommon antibody that is produced by  immature B cells. The exact purpose of this antibody is unknown, though it has something to do with the humoral immune response in humans and other animals. It is similar in function to immunoglobulin M, which is also produced by B cells. Like many other immunoglobulins, IgD is made up of four chains of amino acids. Two heavy and two light chains are connected by a hinge in the middle.