Antigen-Antibody Interactions: an analysis

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Antigen-Antibody Interactions: an analysis

Introduction

Common to all antibodies is the specificity they exhibit in binding to epitopes present on the surface of antigen in which ultimately a lattice formation results due to cross-linking. The present experiment exploits this interaction and is physically observed as agglutination (when antigen is present on a cell) or precipitation (antigen free-floating in solution) (Elek et al., 1964).

Presently, the experiment uses both qualitative and quantitative analyses in order to ascertain the levels of antibodies in sera; such information, for example, is useful in assessing the presence of a current infection in a patient.

More specifically, during Part A, presence of agglutination, due to the interaction between Salmonella H (flagellar) and O (somatic) antigens and the appropriate antibodies, was used as a qualitative measure in order to assess whether the patient is currently infected with Salmonella typhi or paratyphi A strains, a process known as the Widal test (Parry et al., 1999). Part B employed a quantitative analysis to determine the level of precipitation upon interaction between bovine serum albumin (BSA) antigen and antiBSA to allow the determination of the concentration of antibody in an original antiserum sample.

Materials and Method

As per BIOL3141 Infection and Immunity Laboratory Manual 2011 pg 19 -26.

Results

Part A.

The agglutination technique employed presently is the test tube method. Agglutinations were visualised as white particulate matter clumped together at the bottom of the test tubes. The scoring method, from 0 to 4, used presently is that adapted from Olopoenia et al., 1999, where 0 is recorded for no agglutination and 4 for 100% agglutination. Olopoenia et al. 1999 indicates that the smallest quantity of serum that exhibits a score of 2 is considered to be the titre.

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Agglutination was observed only in tubes 1-3 for both serum samples A and B (a titre of 20 for both samples was recorded; see Table 1 in Appendix) when incubated with S. paratyphi A. However, inoculation with S. typhi yielded agglutination in tubes 1-3 inclusive for serum sample A (a titre of 40), whilst tubes up to and including six were positive for agglutination for serum sample B, yielding a titre of 320 (see Table 2 in Appendix). The control tube (10) was absent of agglutination in both scenarios.  

According to Sansone et al., 1972 a four-fold increase in titre is ...

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