A Protein Microarray Assay for Serological Determination of Antigen-specific Antibody Responses Following Clostridium difficile Infection

This method may help with optimizing and selecting clinically useful immunotherapies for Clostridium difficile infection in a patient-specific manner, and elucidating human immune responses to Clostridium difficile. The main advantage of this technique is that it enables accurate and simultaneous quantification of multi isotype and strain-specific antibody responses to C.difficile antigens. Generally, individuals that are new to this method will struggle because expertise is required in establishing and optimizing a panel of highly purified antigens, and setting up the technological platform.

Visual demonstration of this method is critical, as methodological list types involved in preparing the microwave plate, arrays printing, a safe procedure, and the data analysis require attention to the details. Demonstrating some of the procedure will be by Sam Greenwood, a technician from my laboratory. To begin, dilute Clostridium difficile antigens and printing buffer to optimum concentration.

Next, transfer 10 microliters of antigen solution to a 384 well plate. Cover the plate with a plate seal, and centrifuge at 300 times gravity for five minutes at room temperature. For microarray printing, use a hand-held gas burner to heat the silicon PIN three times for two seconds each.

Then, rinse the silicon PIN in clean water three times for three seconds each. Place the microarray plate in the loading cartridge of an arrayer. Eject the tray, and then place the amino silane slides in the slide tray and press the OK button to turn the vacuum on.

Insure that all of the slides are secured, and then click OK.Return the tray to the origin, and close the lid. Next, launch the appropriate program and go to File, then Microarraying Parameters, then Open. Select Clostridium difficile file for printing all antigens in quadruplicate.

Under this window, open the Source tab to indicate sample storage, and Target tab to input microarray details. Then, open the Options tab to select the washing tool. Under the General tab of Run Preferences, on the TAS applications suite toolbar, select Wash at start of run, and Wash at end of run.

Open the Climate tab, and set the humidity level between 55 to 60%Now start the run, and periodically check the arrayer to insure proper functioning. After printing, carefully place the printed slides in a slide holder with 16 multi-well chambers. Then add 100 microliters of 5%BSAT to each block.

Cover the slides and incubate for one hour at room temperature with shaking. Use 120 microliters of PBST to wash each block five times for one minute each with shaking. Next, thaw out the serum samples obtained from C difficile infected patients and healthy controls on ice for 20 minutes.

Add commercially available antibody diluent to the master block, and then add samples to the master block and mix. Discard the washing buffer and add 100 microliters of each diluted sample to the experimental blocks. For the negative control block, add 100 microliters of only the antibody diluent.

Then, incubate the slides for one hour at room temperature with gentle shaking. Next, use 120 microliters of PBST to wash each block five times for three minutes each with shaking. Then add 100 microliters of biotinylated goat anti-Human antibody diluted in antibody diluent to each block.

Cover the slides and incubate for one hour at room temperature with gentle shaking. Use 120 microliters of PBST to wash each block five times for three minutes each with shaking. Next, add 100 microliters of streptavidin SY5 conjugate diluted in 5%BSAT, in a ratio of one to two thousand to each block.

Cover the slides with foil and incubate for 15 minutes at room temperature with gentle shaking. Wash the slides first with 120 microliters of PBST five times for one minute each, and then wash them two more times for one minute each with PBS. To dry the slides, spin them for five minutes at 300 times gravity.

Turn the laser scanner on 30 minutes prior to scanning, to allow it to warm up. Then place the slide in the scanner with the printed surface facing up until the plate light turns solid green. Next, press the Settings button.

On the first tab, insure that the Automatic scrolling and Barcode are unchecked. Then, set the Pixel size to 10, Scan Mode to Medium, Acquisition to 635 only, Acquisition Mode to Manual, gain to 20, and power to low. On the second tab, insure that the slide type is unlabeled.

On the third tab, set the Focus setting to Auto focus. Press the import grid button to select the appropriate array list associated with the scanned image. Then, press the autofind button to align the grid to the spots on the slide.

Finally, press the Quantification Process button to measure the fluorescence intensity of each spot. Then, save the results in an appropriate format for further analysis. In this protocol, a protein microarray is compared with ELISA to assess the reproducibility between these two techniques.

The Spearman correlation coefficient analysis shows significant agreement between the microarray and ELISA for detecting IgG Anti-toxin A, and Anti-toxin B levels in serum samples. Intro assay and inter assay reproducibility of the protein micro array are calculated using the serum samples of seven patients. The samples analyzed on two different array slides against Toxin A, Toxin B, SLP001, SLP002, SLP027, Toxin B from Toxin B only producing strain CCUG, and pCDTb antigens reveal good reproducibility.

A protein microarray is performed to detect an isotype-specific antibody response against Clostridium difficile toxins. The serum samples of patients and healthy individuals are used to detect the levels of IgG and IgA against Toxin A, Toxin B, Toxin B from a Clostridium difficile Toxin B only expressing strain, and precursor form of a B fragment of binary toxin. Once mastered, this technique can be done in seven hours.

The quality control experiment, different parameters such as selection of appropriate surface chemistry, printing buffers, blocking buffers, and dilutions of serum samples and secondary antibodies should be evaluated before running samples. Printing a high-quality array requires a good understanding of the array or software to adjust the printing of parameters according to the experimental protocol. It is crucial to maintain optimum performance of the arrayer, and a dust-free environment throughout the experiment.

This technique will pave the way for researchers in the field of immunology and molecular biology, in terms of characterizing humoral immune responses to infection, and discovering serodiagnostic antigens. Don’t forget that working with infected blood samples and bacterial toxins can be hazardous. In general, in laboratory, safety and standard precautions should always be taken into consideration while performing this procedure.