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Saudi Journal of Kidney Diseases and Transplantation
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EDITORIAL Table of Contents   
Year : 2006  |  Volume : 17  |  Issue : 1  |  Page : 1-4
Panel Reactive Antibody test (PRA) in renal transplantation


College of Medicine & Pathology Department, King Abdulaziz Medical City, Academy for Health Sciences, National Guard Health Affairs, Riyadh, Saudi Arabia

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How to cite this article:
Hajeer AH. Panel Reactive Antibody test (PRA) in renal transplantation. Saudi J Kidney Dis Transpl 2006;17:1-4

How to cite this URL:
Hajeer AH. Panel Reactive Antibody test (PRA) in renal transplantation. Saudi J Kidney Dis Transpl [serial online] 2006 [cited 2017 Feb 23];17:1-4. Available from: http://www.sjkdt.org/text.asp?2006/17/1/1/32436
Our immune response has evolved to counteract foreign antigens, such as viruses and bacteria. Both cellular and humoral antibody responses can be triggered as a result of infection. However, the immune system may undesirably react to non-infectious agents such as food, pollen (allergies) allograft (transplant rejection) and respond to hidden or unhidden self-antigens (auto-immunity).

When exposed to tissues of another person, the immune system mounts a reaction, mainly to the polymorphic (variables or different) antigens of that individual. This is called priming of the immune system to the antigen(s). For example transfusion of plate­lets from an individual with a different class I antigens (constitutively expressed on platelets) will result in priming both arms of the immune response (cellular and humoral) against class I antigens. Organ transplant­tation for such an individual may result in hyperacute rejection.

Priming of the immune response to HLA class I and / or II can occur as a result of pregnancy, blood transfusions or rejection of a previous transplant. [1] However, there are individuals who have HLA antibodies with no history of exposure to the above factors.

This can be explained by the presence of cross-reacting antibodies, usually of IgM class. Leukodepleted blood has been used to reduce the risk of all immunization. How­ever, a randomized trial [2] found that filtration of leukocyte still results in post transfusion alloimmunization, merely because filtration cannot deplete all leucocytes.

Anti-HLA antibodies are usually referred to as panel reactive antibody (PRA) test that sometimes is referred to as percent reactive antibody, since the result is expressed as a percentage.


   How can anti-HLA antibodies cause rejection? Top


Hyper acute rejection

In case of a kidney for example, circu­lating anti-HLA class I antibodies bind to the expressed antigens on endothelial cells resulting in complement activation and cell death. This in turn attracts different immune cells (to the site) such as granulocytes and platelets and the formation of microthombi and necrosis. IgG anti - HLA and ABO antibodies have been shown to cause hyper acute rejection. [3],[4]

Acute Rejection

There is mounting evidence to suggest that acute rejection is caused by both cellular and humoral immune responses. HLA- specific lymphocytes, antibodies, [5] plasma cells [6] and C4d recovered from rejected allografts suggest that both humoral and cellular response act to induce rejection.

Anti HLA antibodies induce rejection not only by activating complement but also through antibody dependent cell-mediated cytotoxicity (ADCC) [5],[7]


   How can we identify anti-HLA antibodies? Top


Complement dependent cytotoxicity (CDC)

CDC was the first technique to detect HLA specific antibodies. It employs the use of live lymphocytes to detect lymphocyte­specific antibodies by activation of comple­ment system and killing of lymphocytes. This is a widely used test, but has many drawbacks, (i) it is limited by the cell panel used, (ii) it depends on the quality of lymphocytes and rabbit complement, (iii) it detects non-HLA antigens and (iv) it only detects complement fixing antibodies. Therefore, patients cannot be tagged as sensitized on the basis of this test. Results are expressed as percentage of cells reacted with the tested serum.


   Elisa Top


The enzyme-linked immunosorbant assay (ELISA) employs the use of HLA antigens, this removes the need for complement, live cells and excludes the non-HLA specific antibodies. [8],[9] There are two types of commercially available kits, one detects presence or absence of PRA, the other detects antibody specificity. PRA detected by ELISA is more sensitive than the CDC assay. [10],[11]

Flow Cytometry

This assay depends on the availability of a flow cytometer in the laboratory. Two different methods can be employed (i) an in house method in which whole lymphocytes are used as the antigens [12],[13],[14],[15],[16] and (ii) comer­cially available kits which employ beads coated with specific HLA- antigens. [17] HLA- A, B, Cw, DR, DQ, and DP coated beads have been used and shown to be much more sensitive than the CDC method. [10]

Advances in this methodology result in the introduction of single antigen coated beads. This method helps identifying the specificity of PRA in highly sensitized patients and improves the definition of acceptable mis­matches. [18]

What method shall our lab use?

It is important not to rely on one method for the detection of PRA as each method has its own advantages and disadvantages.

One can use any of the three methods for screening, but a strategy for defining PRA specificity should be employed. It is advised to use more than one assay in the labora­tory. But one has to keep in mind that the method used for PRA should match in sensi­tivity the method used for crossmatching.


   How often shall we screen for PRA? Top


Pre transplant

Anti-HLA antibodies vary with time in one individual patient and may be influenced by many factors. Therefore, it is recommended to screen patients for PRA in specified intervals. This should not be more than 3 months. In case of blood transfusion, a sample should be sent to the laboratory between 14 to 28 days post transfusion.

If PRA and antibody specificity are determined on a series of patient sera, this can greatly help in predicting the cross­match results. Even in patients who receive zero mismatches at HLA-A, B and DR benefit from regular screening and antibody characterization. Antibody specific to HLA­Cw, DQ and even DP have been shown to influence graft outcome. [19],[20],[21]

Post Transplant

Even though transplant patients receive immunosuppressive drugs, their immune system is still capable of mounting immune responses. De novo antibodies produced post transplant are capable of rejection and chronic graft damage. Monitoring anti - HLA, antibodies post transplant, especially donor specific antibodies, can help in predicting graft outcome. It is recommended that serum samples should be tested for PRA monthly for the first 3 months and quarterly up to one year and annually thereafter. The development of anti - HLA antibodies post transplantation has been shown to be a strong predictor of graft failure.[22] It is therefore necessary to use assays that can detect those antibodies with high sensitivity and specificity such as ELISA and flow cytometry.


   Conclusion Top


The PRA is a very useful marker in renal transplantation. Histocompatibility laboratories should have the sensitive and specific tools to allow for detecting the anti-HLA antibodies formed pre or post transplantation.

 
   References Top

1.Zhou YC, Cecka JM. Sensitization in renal transplantation. Clin Transpl 1991:313-23.  Back to cited text no. 1  [PUBMED]  
2.Van de Watering L, Hermans J, Witvliet M, Versteegh M, Brand A. HLA and RBC immunization after filtered and buffy coat-depleted blood transfusion in cardiac surgery: a randomized controlled trial. Transfusion 2003;43:765-71.  Back to cited text no. 2  [PUBMED]  [FULLTEXT]
3.Williams GM, Hume DM, Hudson RP Jr, Morris PJ, Kano K, Milgrom F. "Hyper­acute" renal-homograft rejection in man. N Engl J Med 1968; 279:611-8.  Back to cited text no. 3  [PUBMED]  
4.Cross DE, Whittier FC, Cuppage FE, Crouch T, Manuel EL, Grantham JJ. Letter: Hyperacute rejection of renal allo­grafts following pulsatile perfusion with a perfusate containing specific antibody. Transplantation 1974;17:626-9.  Back to cited text no. 4  [PUBMED]  
5.Tilney NL, Garovoy MR, Busch GJ, Strom TB, Graves MJ, Carpenter CB. Rejected human renal allografts: recovery and characteristics of infiltrating cells and antibody. Transplantation 1979; 28:421-6.  Back to cited text no. 5  [PUBMED]  
6.Garovoy MR, Reddish MA, Busch GJ, Tilney NL. Immunoglobulin-secreting cells recovered from rejected human renal allo­grafts. Transplantation 1982, 33:109-111.  Back to cited text no. 6  [PUBMED]  
7.Strom TB, Tilney NL, Paradysz JM, Bancewicz J, Carpenter CB. Cellular components of allograft rejection: identity, specificity, and cytotoxic function of cells infiltrating acutely rejecting allografts. J Immunol 1977;118:2020-6.  Back to cited text no. 7  [PUBMED]  [FULLTEXT]
8.Buelow R, Chiang TR, Monteiro F, et al. Soluble HLA antigens and ELISA-a new technology for crossmatch testing. Transplantation 1995; 60:1594-9.  Back to cited text no. 8  [PUBMED]  
9.Kao KJ, Scornik JC, Small SJ. Enzyme­linked immunoassay for anti-HLA antibodies-an alternative to panel studies by lymphocytotoxicity. Transplantation 1993; 55:192-6.  Back to cited text no. 9  [PUBMED]  
10.Worthington JE, Robson AJ, Sheldon S, Langton A, Martin S. A comparison of enzyme-linked immunoabsorbent assays and flow cytometry techniques for the detection of HLA specific antibodies. Hum Immunol 2001; 62:1178-84.  Back to cited text no. 10  [PUBMED]  [FULLTEXT]
11.Zachary AA, Delaney NL, Lucas DP, Leffell MS. Characterization of HLA class I specific antibodies by ELISA using solubilized antigen targets: I. Evaluation of the GTI QuikID assay and analysis of antibody patterns. Hum Immunol 2001; 62:228-35.  Back to cited text no. 11    
12.Harmer AW, Heads AJ, Vaughn RW. Detection of HLA class I- and class II­specific antibodies by flow cytometry and PRA-STAT screening in renal transplant recipients. Transplantation 1997; 63:1828-32.  Back to cited text no. 12  [PUBMED]  [FULLTEXT]
13.Harmer AW, Sutton M, Bayne A, Vaughan RW, Welsh KI. A highly sensitive, rapid screening method for the detection of antibodies directed against HLA class I and II antigens. Transpl Int 1993;6:277-80.  Back to cited text no. 13  [PUBMED]  
14.Lederer SR, Schneeberger H, Albert E, et al. Early renal graft dysfunction. The role of preformed antibodies to DR-typed lymphoblastoid cell lines. Transplan­tation 1996; 61:313-9.  Back to cited text no. 14    
15.Cicciarelli J, Helstab K, Mendez R. Flow cytometry PRA, a new test that is highly correlated with graft survival. Clin Transplant 1992;6:159-64.  Back to cited text no. 15  [PUBMED]  
16.Shroyer TW, Deierhoi MH, Mink CA, et al. A rapid flow cytometry assay for HLA antibody detection using a pooled cell panel covering 14 serological crossreacting groups. Transplantation 1995; 59:626-30.  Back to cited text no. 16  [PUBMED]  
17.Sumitran-Karuppan S, Moller E. The use of magnetic beads coated with soluble HLA class I or class II proteins in antibody screening and for specificity determinations of donor-reactive anti­bodies. Transplantation 1996; 61:1539-45.  Back to cited text no. 17  [PUBMED]  [FULLTEXT]
18.Pei R, Lee JH, Shih NJ, Chen M, Terasaki PI. Single human leukocyte antigen flow cytometry beads for accurate identification of human leukocyte antigen antibody specificities. Transplantation 2003; 75:43-9.  Back to cited text no. 18  [PUBMED]  [FULLTEXT]
19.Mytilineos J, Deufel A, Opelz G. Clinical relevance of HLA-DPB locus matching for cadaver kidney retransplants: a report of the Collaborative Transplant Study. Transplantation 1997;63:1351-4.  Back to cited text no. 19  [PUBMED]  [FULLTEXT]
20.Takemoto S, Cecka JM, Gjertson DW, Terasaki PI. Six-antigen-matched trans­plants. Causes of failure. Transplan-tation 1993; 55:1005-8.  Back to cited text no. 20    
21.Chapman JR, Taylor C, Ting A, Morris PJ. Hyperacute rejection of a renal allograft in the presence of anti-HLA-Cw5 antibody. Transplantation 1986; 42:91-3.  Back to cited text no. 21  [PUBMED]  
22.Worthington JE, Martin S, Al-Husseini DM, Dyer PA, Johnson RW. Post­transplantation production of donor HLA-specific antibodies as a predictor of renal transplant outcome. Transplan­tation 2003,75:1034-40.  Back to cited text no. 22    

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Correspondence Address:
Ali H Hajeer
College of Medicine Academy for Health Sciences King Abdulaziz Medical City P. O. Box 22490, Riyadh 11426
Saudi Arabia
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PMID: 17297529

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