Sanjay Gandhi PGIMS, Lucknow Correlation between the IgG subclasses with occurrence and severity of haemolytic disease of fetus and newborn Bharat Singh, Rahul Katharia, Mandakini Pradhan, Rajendra Chaudhary Sanjay Gandhi PGIMS, Lucknow

Background Hemolytic disease of fetus and newborn(HDFN)- Decreased life span of red blood cells (RBCs) due to accelerated destruction Primarily caused by Maternal alloimmunization against paternal red cell antigens Anti-D is most commonly involved antibody(78% cases) Without proper management 50% affected fetus would succumb to death. Could lead to loss or damage of approximately 50,000 foetus per year. HDFN occurrence and severity depends on multiple factors. IgG subclass is one of these factors.

HDFN- Pathophysiology

IgG subclasses in HDFN IgG Antibody in HDFN- Capable of crossing the placenta. Responsible for HDFN Subdivided into four subclasses- IgG1, IgG2, IgG3 and IgG4 IgG subclasses exhibit differences in properties- Characteristic IgG1 IgG2 IgG3 IgG4 Ability to cross placenta + ± Complement Fixation ++ +++ - Binding to macrophage FcR

Aims and objectives To correlate the IgG subclass with occurrence and severity of Hemolytic Disease of Fetus and Newborn (HDFN) To study the prevalence of IgG subclasses (IgG1 and IgG3) in antenatal alloimmunized women in North India

Material and Methods Prospective observational study 48 alloimmunized (with anti-D alone) antenatal cases were studied. “DAT IgG1/IgG3 ID” card (Bio-Rad) was used for IgG subclass determination. Pregnancies were followed–up to see the outcome. Pregnancy outcome was classified into unaffected/ mild-moderate/ severe HDFN. Subclass prevalence was calculated and HDFN severity was correlated with IgG subclass in the study population.

Result # Distribution of IgG subclass among various grades of severity (n=48) (Prevalence) Unaffected Mild - Moderate Severe IgG1 (n=12, 25%) 2 (16.6%) 04 (33.3 % ) 06 (50%) IgG1+IgG3 (n=20, 41.6%) 3 (15%) 04 (20 %) 13 (65 %) IgG3 (n=09, 18.7%) 4 (44.4%) 03 (33.3 %) 02 (22.2 %) No IgG1/IgG3 (n=07, 14.5%) 6 (85.7%) 1 (14.3%) 0 (0%)

Results # HDFN occurrence and severity Significantly higher when- IgG1 was present alone or in combination with IgG3 (p value < 0.01). Lowest in patients with neither IgG1 nor IgG3 The risk of severe HDFN was 9.5 times higher when IgG1 was present IgG1 (alone or in conbnation)>IgG3>Neither IgG1 nor IgG3

Discussion Occurrence severity of HDFN is determined by various factors. Association between IgG subclass and the severity of HDFN- A debatable issue due to conflicting outcome seen in various studies. In the majority of studies- Antibodies to the Rh system antigens are mostly of the IgG1 and IgG3 subclasses Subclasses IgG1 and IgG3 are more efficient at causing hemolysis IgG1 > IgG3 > IgG2 & IgG4

Some Other studies Author Subclass prevalence Predictive value of IgG subclass in HDFN Emilija Velkova, 2015 IgG1- 35.5, IgG3- 6.66, IgG1+IgG3- 57.7 No Pollock JM et al, 1990 IgG1- 32.6, IgG3- 3.06, IgG1+IgG3- 64.2 Yes (IgG1+IgG3>IgG1>IgG3) Y.S. Iyer et al, 1992 IgG1-53.2 , IgG3- 12.1, IgG1+IgG3- 21.5 Neither IgG1 nor IgG3- 13 (IgG1+IgG3>IgG1>IgG3 >neither IgG1 nor IgG 3) J. Choudhuri et al, 2016 IgG1- 20, IgG3- 3.5, IgG1+IgG3- 24.7, Neither IgG1 nor IgG3- 51.7 ( IgG1 &/or IgG3 >> neither IgG1 nor IgG3) Present study, 2018 IgG1- 24, IgG3- 16.6, IgG1+IgG3- 41.6, Neither IgG1 nor IgG3- 14.5 ( IgG1 ± IgG3 > IgG3 > neither IgG1 nor IgG3)

Discussion From the present and other related studies, we conclude- IgG1/IgG3 subclass increases occurrence & the severity of HDFN significantly . These mothers require closer antenatal monitoring, and neonates require closer follow up to allow for appropriate and timely intervention. IgG subclass determination can be used as an independent prognostic marker for HDFN outcome. The determination of IgG sub-classes is also important when there is a clear discrepancy between serological findings and clinical presentation of HDFN. The present and other studies suggest that subclass determination should be included in a multi – parameter protocol for prediction of the HDFN outcome.