Immunology Questions and Answers – Antibody Assays – ELISA

This set of Immunology Multiple Choice Questions & Answers (MCQs) focuses on “Antibody Assays – ELISA”.

1. What does ELISA stand for?
a) Enzyme-linked immunodeficient sorbent assay
b) Enzyme-linked immunosorbent assay
c) Enzyme-linked immune sorbent assay
d) Enzyme-linked immunity scientific assay
View Answer

Answer: b
Explanation: ELISA is the short form of Enzyme-linked Immunosorbent Assay. Another short form usually used is EIA. This technique is widely used for detection and measurement of antibodies and their presence in blood. If a patient is infected by some bacteria or virus, this technique is used to check whether there has been a development of antibodies against that particular bacteria or virus that causes infections. 

2. Which of the following disease is NOT diagnosed by ELISA?
a) Lyme disease
b) Rotavirus
c) Syphilis
d) Flu
View Answer

Answer: d
Explanation: Normal flu can be treated and diagnosed by medications and does not require any test. On the other hand, Lyme disease (caused by bacteria Borrelia burgdorferi), Rotavirus (viral infection-most common in children) and Syphilis (which is sexually transmittable) are some of the serious infections and diseases which need to be detected by ELISA to check for presence and behaviour of antibodies.   

3. ELISA is divided into 4 categories namely: Direct, Indirect, Competition and Supplementary ELISA.
a) True 
b) False
View Answer

Answer: b
Explanation: It is true that ELISA technique is categorised into 4 major sections but these sections are Direct, Indirect, Competition and Sandwich ELISA. These techniques are used for various respective motives. There is no such category named as Supplementary ELISA. Direct ELISA is much faster in mechanism as it has limited steps. The Indirect ELISA technique is highly sensitive and it involves indirect interaction of enzyme labelled antibody to primary antibody. Sandwich ELISA shows the involvement of paired antibodies whereas in Competition ELISA involves the assay techniques which involves inhibition as well as blocking the competitive antibody.  

4. With which of the following enzyme, labelling of antibodies is carried out in Direct ELISA detection technique?
a) Alkaline Phosphatase
b) Hyaluronidase
c) Lactase
d) Amylase
View Answer

Answer: a
Explanation: Direct ELISA technique involves labelling of enzyme linked antibodies which is mediated by Alkaline Phosphate (AP) as it gives a rapid colorimetric output when observed via spectrophotometer. This technique falls under the category chromogenic assay. Alkaline phosphatase that is derived from Escherichia coli has an optimum activity at pH 8.0 whereas the AP obtained from calf intestines has optimal pH at 9.6. It is observed that the stable nature of AP is far more applicable and accurate. 

5. Which of the following ELISA kits are available for specific purposes?
a) Antibody pair kit and Instant ELISA kit containing post-coated antibody plates
b) Inferior ELISA kit and Antigen pair kit
c) Antibody pair kit and Instant ELISA kit containing pre-coated antibody plates
d) Instant ELISA kit and Inferior ELISA kit
View Answer

Answer: c
Explanation: The two types of ELISA kits that are the most specific are 1) Instant ELISA kit containing pre-coated antibody plates. This kit includes only the capture antibody which in presence of the sample contain the essential constituents like the capture antibody and lyophilized detection antibody. 2) Antibody pair kits that are made up of individual matched antibodies and standard devoid of plates and reagents for detection. These kits are all are ready to use and are offered in several formats as well as quantitative, semi-quantitative, indirect or competitive. 

6. Which of the following is an important disadvantage of Indirect ELISA?
a) Optimization in terms of antibody becomes problematic due to cross-reactivity issues
b) Higher signal to noise ratio results in issues of accuracy
c) For recognition of a specific epitope, only monoclonal antibodies can be applied as matched pairs
d) Offers less flexibility in terms of primary antibody
View Answer

Answer: b
Explanation: Indirect ELISA technique is widely used which has one of the most important motive of employing enzyme labelled secondary antibody to be interacted with a primary antibody. Indirect ELISA is in a greater demand as compared to direct ELISA as indirect ELISA offers an easy to carry out the entire method with ease as it fulfils the requirement of the needed number of labelled antibodies. There are various advantages in support of indirect ELISA but the most important disadvantage that is observed includes issues faced due to high ratio of signal to noise. This can result in inaccurate results. This technique is also time-consuming.   

7. Immobilisation of antibody-antigen is mediated by which type of interaction?
a) Hydrophilic interaction
b) Hydrophobic interaction
c) Non-covalent interaction
d) Chemical interaction
View Answer

Answer: b
Explanation: Antibody-antigen interaction is hydrophobic hence their immobilization is mediated by hydrophobic interactions only. Their interaction can also be covalent depending upon the valency of both, antigen and antibody. It also depends on the size of these molecules that perform immobilization in order to interact with one another. Usually, proteins are preferred in such cases as they show a great and quick response during immobilisation due to their ions.  

8. Which antibodies are used for ELISA technique?
a) Primary antibodies
b) Secondary antibodies
c) Primary as well as secondary antibodies
d) Primary, secondary and tertiary antibodies
View Answer

Answer: c
Explanation: Antibodies are used to determine the expression levels and localization of molecules of interest. The selection of antibodies depends on various factors like its clonality, source of the antibody, its isotype as well as its primary application. On the basis of these factors, antibodies are divided into two main types in order to understand their similarities and differences as well as to avoid confusion—primary and secondary antibodies. 

9. Which of the following is NOT a type of data output expected in ELISA assay?
a) Quantitative analysis
b) Qualitative analysis
c) Semi-quantitative analysis
d) Semi-qualitative analysis
View Answer

Answer: d
Explanation: ELISA assay technique involves a number of steps. However, calculation of results and observations are two of the most important concluding steps of ELISA. There are different sections under which the output can be framed. These are as follows: 1) Quantitative (includes standard curve graph by knowing the concentration of antigen), 2) Qualitative (to observe the presence or absence of the antigen in comparison to the control) and 3) Semi-quantitative (includes observation of number of antigens by comparing it with other samples).  

10.  Which of the following is NOT an advantage of Sandwich ELISA?
a) Offers high sensitivity compared to direct or indirect ELISA
b) Introduces highly specific reaction due to the involvement of two antibodies for antigen detection
c) Both direct and indirect technique is implemented in detection
d) It is cheaper as there is a requirement of fewer labelled antibodies
View Answer

Answer: d
Explanation: Sandwich ELISA promotes the usage of antibody pairs such as capture antibody and detection antibody which can be a monoclonal or polyclonal antibody. Each antibody is highly specific towards epitope of an antigen and the assay is found to be more suitable for antigens possessing two epitopes. The specificity of matched antibody pairs is very important to confirm their binding to different epitopes in obtaining precise results. Hence it is highly specific and sensitive.  As its name suggests, the capture antibody interacts with an antigen which can then be detected via both direct and indirect ELISA techniques. This technique is not cheap as it requires high maintenance.

11. What is the optimal range (moles/lit) for proteins to be detected by ELISA assay?
a) 102 to 106 moles/lit
b) 10-12 to 10-9 moles/lit
c) 1012 to 109 moles/lit
d) 10-2 to 10-6 moles/lit
View Answer

Answer: b
Explanation: ELISA technique is a widely used and accepted technique for various motives including for the study of viruses and for its diagnosis. It uses mainly proteins as they are reactive and have a greater response. ELISA helps in detecting these proteins at a range of 10-12 to 10-9 moles per litre. This is usually measured in a range of picomolar to nanomolar.   

Sanfoundry Global Education & Learning Series – Immunology.

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Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He lives in Bangalore, and focuses on development of Linux Kernel, SAN Technologies, Advanced C, Data Structures & Alogrithms. Stay connected with him at LinkedIn.

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