antibodies are secreted by a type of white blood cells called plasma cells, whereas WBC are secreted by red marrow..

It is not correct, or at least is too vague as statement.

Antibodies are "de novo" synthesised by the immune system (check the mechanism of protein synthesis on the books), while what you eat is metabolised by your body and used for all functions.

Essentially everything that is produced in the body has it's origin in the food. Proteins are typically degraded to amino acids which then serve as building blocks for new proteins. Whereas the backbone of essential amino acids is kept intact (with some modifications to made other amino acids) one can expect that a certain amount of non-essential acids is completely broken down (for energy production) and newly synthesized when needed.

As some amino acids from the food will end up in the antibodies (and every other protein in the body) your statement is not wrong but as correct as saying "The bread I eat will end up in antibodies".

The dietray protein or the protein that we eat gets digested, degraded, and is deposited into the "nitrogen or amino acid pool" which is a mixture of amino acids. Proteins and amino acids are not saved or stored in the body so there is a continuous synthesis of some proteins and those which cannot be synthesized by the body, need to come from the food or the supplements we take. While some proteins are being replenished, those which are already in our system are continually degraded or destroyed. In the case of enzymes, for instance, these are recycled in minutes or hours while plasma proteins have a half-life of 180 days or more. While these are going on, some of the amino acids in the pool are destroyed into energy and ammonia which is converted to urea and is lost in the urine. This process ultimately decreases the nitorgen pool.

Hence, whatever protein you take in gets digested down to the bare backbone of proteins which are the amino acids. At the same time, some amino acids are synthesized by the body. When proteins such as antibodies get produced by the body, they do not necessarily resemble the antibodies you ate anymore because those had been digested to amino acids whichgo into the pool. The antibodies produced by your body uses both the amino acids that were synthesized and those that came from digested food.

If you want the non-inherrent antibodies to function in your system, do not eat them. Instead, administer them through injection so that they can avoid digestion to a certain extent. However, any foreign material that goes into our blood stream will be acted upon by the immune system and maybe ingested/destroyed by the macrophage cells. Thus, when we want to produce antibodies, we get injected by the antigen as in vaccinations.

You can look at the diagram for the fate of dietary protein at this URL

http://www.elmhurst.edu/~chm/vchembook/630proteinmet.html

Matthias Pietzke & Zoraida Aguilar answers are right . Some amino acids from the food will end up in the antibodies (and every other proteins in the body) your statement should be corrected..