Structure-function relationships of the antigenicity of mycolic acids in tuberculosis patients.
Cell wall mycolic acids (MA) from Mycobacterium tuberculosis (M.tb) are CD1b presented antigens that can be used to detect antibodies as surrogate markers of active TB, even in HIV coinfected patients. The use of the complex mixtures of natural MA is complicated by an apparent antibody cross-reactivity with cholesterol. Here firstly we report three recombinant monoclonal scFv antibody fragments in the chicken germ-line antibody repertoire, which demonstrate the possibilities for cross-reactivity: the first recognized both cholesterol and mycolic acids, the second mycolic acids but not cholesterol, and the third cholesterol but not mycolic acids. Secondly, MA structure is experimentally interrogated to try to understand the cross-reactivity. Unique synthetic mycolic acids representative of the three main functional classes show varying antigenicity against human TB patient sera, depending on the functional groups present and on their stereochemistry. Oxygenated (methoxy- and keto-) mycolic acid was found to be more antigenic than alpha-mycolic acids. Synthetic methoxy-mycolic acids were the most antigenic, one containing a trans-cyclopropane apparently being somewhat more antigenic than the natural mixture. Trans-cyclopropane-containing keto- and hydroxy-mycolic acids were also found to be the most antigenic among each of these classes. However, none of the individual synthetic mycolic acids significantly and reproducibly distinguished the pooled serum of TB positive patients from that of TB negative patients better than the natural mixture of MA. This argues against the potential to improve the specificity of serodiagnosis of TB with a defined single synthetic mycolic acid antigen from this set, although sensitivity may be facilitated by using a synthetic methoxy-mycolic acid.
Beukes
Mervyn
M
Department of Biochemistry, University of Pretoria, South Africa.
Lemmer
Yolandy
Y
Deysel
Madrey
M
Al Dulayymi
Juma'a R
JR
Juma'a
R Al Dulayymi
RA
Baird
Mark S
MS
Mark
S Baird
SB
Koza
Gani
G
Iglesias
Maximiliano M
MM
Maximiliano
M Iglesias
MI
Rowles
Richard R
RR
Richard
R Rowles
RR
Theunissen
Cornelia
C
Grooten
Johan
J
Toschi
Gianna
G
Roberts
Vanessa V
VV
Vanessa
V Roberts
VR
Pilcher
Lynne
L
Van Wyngaardt
Sandra
S
Mathebula
Nsovo
N
Balogun
Mohammed
M
Stoltz
Anton C
AC
Anton
C Stoltz
CS
Verschoor
Jan A
JA
D000818:Animals; D000906:Antibodies / Q000097:blood / Q000276:immunology; D000911:Antibodies, Monoclonal / Q000276:immunology; D000942:Antigens, Bacterial / Q000737:chemistry* / Q000276:immunology; D002645:Chickens; D002784:Cholesterol / Q000737:chemistry / Q000276:immunology; D003429:Cross Reactions; D004797:Enzyme-Linked Immunosorbent Assay; D006801:Humans; D009169:Mycobacterium tuberculosis / Q000737:chemistry; D009171:Mycolic Acids / Q000138:chemical synthesis / Q000737:chemistry* / Q000276:immunology; D019151:Peptide Library; D012698:Serologic Tests; D057127:Single-Chain Antibodies / Q000276:immunology; D014376:Tuberculosis / Q000175:diagnosis* / Q000276:immunology
D000906:Antibodies; D000911:Antibodies, Monoclonal; D000942:Antigens, Bacterial; D009171:Mycolic Acids; D019151:Peptide Library; D057127:Single-Chain Antibodies; D002784:Cholesterol