## 3 Results
#### 3.1.3 Differences in the Resolution with and the Sensitivity of the Detection Abs  
The MFI levels of the sera Abs tested at a particular dilution (1:10) measure the binding affinity of the anti-HLA Abs. The MFI of the anti-HLA Abs that are reactive on both the SABs (Figure 2) also differs with different detection Abs. The MFI values obtained using FC-binding monoclonal IgG are consistently higher than the MFI obtained with IgG heavy chain-binding polyclonal Fab fragments. The MFI obtained for anti-HLA Abs against HLA-I alleles are frequently higher with _FcMonolgG_;  
Several sera Abs (e.g., 3 LE, 7 HN, 13 LE, 14 HN), with a high MFI with _FcMonolgG_, were too low or negative with _IgHPolyFab_, with both LS and LC;  
Some sera Abs (e.g., 14 HN, 5 DM, 2 DM, 6 FC), though positive with _IgHPolyFab_ (Figure 2), had MFIs with _FcMonolgG_ that were consistently higher with LC-SAB;  
Several sera (e.g., 3 LE, 11 DM, 13 LE 15 NA, 17 LE, 18 PK) anti-HLA-II Abs (Figure 3), when positive on both SABs, also showed a very high MFI with _FcMonolgG_ (bold values), while the reactivity with _IgHPolyFab_ was low or negative with both LC and LS. In addition to HLA antigens that are common to both SABs, few antigens are unique to either LS or LC (data not presented). For HLA-I antigens on LS-SAB, 38 MFI values were obtained, of which 30 were higher with _FcMonolgG_. On LC-SAB, 38 MFI values were obtained, of which 34 were higher with _FcMonolgG_;  
For HLA-II antigens on LS-SABs, 12 sera tested positive. Of the 45 MFI values obtained with these sera, 43 MFIs were markedly higher with _FcMonolgG_. On LC-SABs, all the 27 MFI values obtained with the nine sera were remarkably higher, only with _FcMonolgG_. Inference: _FcMonolgG_ enhances the resolution and sensitivity of the detection of HLA Abs on both the SABs much better than _IgHPolyFab_. Rarely, higher MFIs with _IgHPolyFab_ were observed, only on LS-SAB. The sera may be poorly sensitized, as in 16 HN (B*15:12/27:5/42:01/59:01, Figure 2B), or highly sensitized, as in 6 FG (C:03:03, Figure 2A), 19 HN (B*40:02/41:01, Figure 2A; B*67:01, Figure 2B), 1 DM (A*01:01/23:01/24:02/40:02/41:01, Figure 2A; B* 67:01, Figure 2B), and 5 DM (A*23:01/24:02/24:03 in the serum of 5 DM, Figure 2A). Similarly, the positive MFIs for Abs against HLA-II, with a _IgHPolyFab_ concomitant with low or negative values, were observed with _FcMonolgG_ on LS-SAB for DQBI*04:02\(\backslash\)DQA1*02:01 (e.g., sera # 5F47, 9M33 and 15F43). Inference: These exceptions observed on LS-SAB could be due to the presence of an OC on the LS, and a lack of the same in LC. Figure 4 summarizes the disparity based on the total sum and mean MFI of IgGs reacting to HLA-I antigens in the four different categories of tests (LC and _FcMonolgG_; _LC_ and _IgHPolyFab_; LS and _FcMonolgG_; and LS and _IgHPolyFab_). Both the sum and mean MFI values of the anti-HLA-I Abs in group 2 and 3 (moderately or highly sensitized groups) are persistently higher with LC than with LS when tested with _FcMonolgG_. All three groups combined are strikingly higher with LC than with LS when tested with _FcMonolgG_;  
With LC-SAB, the sum and mean MFI values for HLA-I Abs assessed using _FcMonolgG_ are 4.4-fold higher than with _IgHPolyFab_; whereas, with LS-SAB, the reactivity with _FcMonolgG_ is just 2.2 to 2.4 higher than that of _IgHPolyFab_;3. In poorly sensitized patients, the sum and mean MFIs are higher with LS than with LC when tested with _FcMonolgG or IgHPolyFab_. The MFIs with both the SABs with _IgHPolyFab_, though almost half of the values were obtained with _FcMonolgG_, were higher with LS than with LC;
4. Similarly, both the sum and mean MFIs of all anti-HLA-II reactivity with _FcMonolgG_ are significantly enhanced four-fold, relative to _IgHPolyFab_;
5. The maximum MFI observed with _FcMonolgG_, compared to _IgHPolyFab_, is higher for LC. Inference: It is evident that _FcMonolgG_ enhances the sensitivity of the SAB immunoassay-say, particularly while monitoring anti-HLA Abs in the sera of highly sensitized patients.