The following describes your patient’s clinical presentation: A 19-year-old Cauc

Question

The following describes your patient’s clinical presentation:

A 19-year-old Caucasian female in her first year at University presented in A&E with confusion, irritability, marked neck stiffness, petechial rash and a body temperature of 38.5oC. In the preceding 24h, the patient had experienced a severe occipital headache with vomiting. A CSF sample was then obtained by lumbar puncture and analysed and the results obtained are shown in Table A:

Table A: Results of the analysis of the patient’s CSF sample

Parameter measured

Result

Reference range

Appearance

Cloudy & turbid

Clear & colourless

Protein

5.2 g/L

0.2 – 0.4 g/L

Glucose mmol/L

0.18 mmol/L

3.3 – 4.4 mmol/L

White cells

4800 x 106/L

97% neutrophils

0 – 5 x 106/L

All lymphocytes

No neutrophils

Red Cells

6.2 x 106/L

0 – 10 x 106/L

Microbiology

Positive for Neisseria meningitides

N/A

The patient was treated with intravenous cefotaxime and made a full recovery. The patient then reported a previous N. meningitides infection at aged 13 years with N. meningitides serogroup Y so, following recovery, further investigations were undertaken to evaluate her immune function. The results obtained are presented in Table B:

Table B: Results of immune screen

Parameter

Result

Reference Range

Serum IgG

12.1 g/L

6.0 – 16.0 g/L

Serum IgA

2.8 g/L

0.8 – 4.0 g/L

Serum IgM

1.2 g/L

0.5 – 2.0 g/L

AH50

0 units

80 – 200 units/mL

CH50

0.6

100- 500 units/mL

***the patient suffers from complement deficiency

Based on the above and in light of the results you have obtained, what possible underlying cause(s) have led to the patient’s reduced resistance to N. meningitides? Explain your rationale.

Parameter measured

Result

Reference range

Appearance

Cloudy & turbid

Clear & colourless

Protein

5.2 g/L

0.2 – 0.4 g/L

Glucose mmol/L

0.18 mmol/L

3.3 – 4.4 mmol/L

White cells

4800 x 106/L

97% neutrophils

0 – 5 x 106/L

All lymphocytes

No neutrophils

Red Cells

6.2 x 106/L

0 – 10 x 106/L

Microbiology

Positive for Neisseria meningitides

N/A

Explanation / Answer

The Complement system functions in both innate and adaptive immunity.It plays a very important role in defence against microbes and in pathologic inflammatory reactions.the system consists of more than 20 proteins, some of which are numbered C1 through C9.

In the process of complement activation, several cleavage products of complement proteins are expressed which cause increased vascular permeability,chemotaxis and opsonization.

the critical step in complement activation is proteolysis of C3.this cleavage of C3 can oocur by

1.The classical pathaway- triggered by fixation of C1 to antibody that has combined with antigen.

2.The alernative pathway-triggered by microbial surface molecules(endotoxins or LPS),complex polysaccarides, and other sunstances in the absence of antibody

3.The Lectin pathway-plasma mannose-binding lectin binds to carbohydrates on icrobes and directly activates C1

all three pathways lead to formation of active enzyme caled the C3 convertase which splits C3 into C3a and C3b.

Neisseria meningitidis(Nm) is a gram-negative diplococcus, whose biochemical characteristics include catalase and oxidase positivity and the ability to ferment glucose and maltose. Almost all invasive isolates of Neisseria meningitidis express capsular polysaccharide. Based on the chemical composition of its capsule, meningococci are divided into 12 groups (A, B, C, E [formerly called 29E], H, I J, L, W [formerly W135], X, Y, and Z). The majority of invasive infections worldwide are caused by six of these groups—A, B, C, W, X, and Y. Antigenic variability of the porin B (PorB) and PorA molecules expressed define the organisms serotype and serosubtype, respectively. Because of limited availability of typing and subtying monoclonal antibodies, high-throughput gene sequencing is now commonly used to classify meningococci for epidemiologic studies.like all gram-negative bacteria, meningococci possess lipopolysaccharide (LPS). However, because the LPS of Nm lacks the O-antigenic repeats seen in common enteric gram-negative bacilli, it is often referred to as lipooligosaccharide (LOS).

complement killing of Nm is the recruitment of the AltenativePathway following antibody-initiated complement activation. Several antibodies, including those directed against the vaccine antigen factor H-binding protein (fHbp), require recruitment of the AltenativePathway and stabilization of the Alt,Pathway C3 convertases by properdin, for maximal killing. The requirement of an intact AltPathawy for killing by some antibodies may explain why persons with AP defects are predisposed to Nm infections.

The requirement for protection through membrane attack complex appears to be unique for Nm and for disseminated gonococcal infections; terminal complement deficient patients are not at a greater risk for contracting other gram-negative infections. High incidence of invasive meningococcal disease in persons with terminal complement deficiencies (C5 through C9).

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