Target of interest
First of all, try to learn as much as possible about your target of interest. A good way to start is by looking in genomic databases such as GeneCards (or similar sites, depending on which species you work with). Collect information about alternative names for your protein or gene. When searching for antibodies, it is advisable to search for both gene and protein names as well as synonyms.
When comparing antibodies, it may useful to learn which part of the protein the antigen is directed against. This is especially important when your protein has several isoforms, to verify that the antibody will recognize the isoform you wish to study. Many providers include the antigen sequence in their product data.
Try to learn as much as possible about your samples. Do you know anything about the level of expression of the target protein in your samples? Is there RNA or mass spectrometry data available for your tissue or cell samples?
Human Protein Atlas
To learn more about your protein of interest and to investigate antibody performance, you may look at your protein on the Human Protein Atlas (HPA) portal. The academic HPA project was established to allow for a systematic genome-based exploration of the human proteome using antibody-based proteomics. Today, 14,100 human proteins have been characterized in a multitude of human normal- and cancer-tissue samples using immunohistochemistry (IHC), Western Blot (WB) and immunofluorescence (IF). The obtained results were then compared with existing literature. The antibodies used in the annotation of the proteins are both in-house produced and supplied by external suppliers, and they are listed with IHC, IF and WB images side by side.
The goal of the HPA project is to compare staining results from several antibodies directed against different regions of the same target protein in human tissues and cells. If the antibodies show the same or a similar staining pattern, the reliability of the antibodies is enhanced. This is of great importance when literature describing tissue and subcellular location of the target proteins is limited.
Application/Species
When searching for antibodies against your protein of interest, you can first narrow your search by filtering for antibodies recommended in the applications and species you work with. You may also take into consideration which host the antibody is raised in, with an eye to your experimental setup. Depending on the application you want to use, there also may be advantages or disadvantages with polyclonal and monoclonal reagents, respectively.
If you are not able to find information about tested species reactivity, you can look for published articles about experiments in which the antibody has been used and contact the company and ask for more information. Comparing antigen sequence identity between the antibody of interest and the corresponding ortholog can provide an indication of whether or not the antibody will recognize the intended target in your species.
Listing sites
There are many sites that list antibodies from different suppliers. These sites often offer convenient ways to compare antibodies by showing images and product specifications in parallel. It is usually possible to filter by application and/or species reactivity as well as other criteria.
Publications and reviews
Investigate whether there are any published references and/or reviews for the antibodies in which you are interested. Do other researchers find the antibodies reliable? Which applications and species have the antibodies been used in?
Using these tips will improve your chances of finding antibodies specifically tailored to your needs.