Katherine Burke

Who I Am

The aim of the study is to give a brief introduction into:

• What I mean by mannose-binding lectin (MBL)• The clinical features of deficiency• How to test for MBL• The significance of MBL (if any)

Aim

Background MBL was first found in baker’s yeast as a

plasma In 1968 there was a case report of a child

with recurrent infections due to a deficiency – although MBL was unknown at the time

1987 saw that MBL was recognised to activate complement

Since then research has been increasing on the subject and yet still much is unknown

What MBL is MBL is a plasma glycoprotein in the collectin family MBL is part of the innate immune system It is commonly known now to activate the complement system through the lectin pathway In humans, MBL normal

forms 1-6 subunit oligomers

The more subunits the stronger the bonding to the microbe

C-Terminal

MutationsMutation Codon Base Change Amino Acid

ChangeB 54 GGC GAC Gly AspC 57 GGA GAA Gly GluD 52 CGT TGT Arg Cys

Two of the mutations occur in the collagen-like domain (B and C)

The third (D) mutation prevents dioligomers to form thus creating poorly functional MBL

(A) would represent the wild type (or ‘normal’)

Clinical Features The main clinical feature would be to

have recurrent infections The research done on MBL has also

concentrated on recurrent respiratory infections in particular

The clinical features were collected by doing a case study of 7 patients that were deficient and then comparing some categories to controls with high MBL

As MBL deficiency is genetically based, it was important to find out any family history

Clinical Features

Family History

Investigations

MBL ELISA ELISA (enzyme-linked

immunosorbent assay) is the method used to test for MBL deficiency

The principle is that MBL if present will bind to antibodies, then antibodies with enzymes will attach onto this

Substrates will bind it enzymes and then this is produce a colour intensity, which can be measured to see if there is any MBL present

The results are compared to a standard curve and high and low controls

The idea is that the amount of substrate is directly proportional to the amount of MBL in the given sample

1hr

1hr

1hr

15m

Wash x3

Wash x3

Wash x3

If the results are more than 1300 ng/mL, the patient has normal alleles with no risk of recurrent infections

If the value is between 400-1300 ng/mL, the patient has a mild deficiency with some risk of recurrent infections

It also shows that the patient is heterozygous for MBL However, if the patient has a value between 75-399.99 ng/mL, then the patient has a

functional deficiency of MBL with an increased risk of recurrent infection If the value is less than 75 ng/mL, the patient is mutant homozygous without functional

MBL These patients would have the greatest risk of recurrent infections

If the results are more than 1300 ng/mL, the patient has normal alleles with no risk of recurrent infections

If the value is between 400-1300 ng/mL, the patient has a mild deficiency with some risk of recurrent infections

It also shows that the patient is heterozygous for MBL However, if the patient has a value between 75-399.99 ng/mL, then the patient has a

functional deficiency of MBL with an increased risk of recurrent infection If the value is less than 75 ng/mL, the patient is mutant homozygous without functional MBL These patients would have the greatest risk of recurrent infections

Treatment

Generally, the treatment for an MBL deficiency is difficult is assess Most of the individuals were mostly healthy

The MBL deficiency only detected when the immune system is compromised already Treatment mainly consisted of antibiotics (in winter) and for the other problems

Conclusions (1) In conclusion, MBL deficiency is

genetically based The main features of this would be

that a patient would have recurrent infections

To test for this one would use the technique ELISA

This would show to what extent a patient was deficient if at all although it would not show the alleles that were mutant or the wild type

Conclusions (2) There has been research to show there is

an advantage of having a MBL deficiency but more research needs to be done into this

Generally, an MBL deficiency would lead to an increased risk of recurrent infections and therefore is treated with antibiotics

However, there is a possibility that a replacement therapy may be available soon

Clinically, it is significant to explain why a patient has recurrent infections and to treat it accordingly

I’d like to thank a few people that made this project possible and helped me along the way:

• Dr. Sonny Chong who thought of the project• Dr. Grant Hayman who also helped think of the

project• Alex Nichols who was kind enough to do the lab work

with me• Dr. Hany Banoub• Imran Bhatia• The kind staff in the immunology lab• The lovely secretaries in paediatrics without whom I

would have been lost on countless occasions• Denise Balmer who organised the Nuffield Bursary

placement• Dr. Sheikh who introduced me to the scheme

Acknowledgements